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At present, regarding to the machining of aspheric lens mold, there are two major methods to carry out the on-machine measurement (OMM) — contacting method (CM) and non-contacting method (NCM). Here such two methods are reviewed in detail. CM is mainly based on the contacting probe which is scratching aspheric surface of lens mold to achieve profile data. To be efficient, an idea with 45° tilt of probe is proposed for OMM of lens mold by Suzuki. But generally speaking, the contacting OMM is not so efficient and can only deal with axisymmetric aspheric lens mold. On the contrary, NCM mostly uses laser to achieve aspheric profile without any contact. On ultra-precision lathe, laser scanning system or laser interferometer is mounted on the frame of lathe and transfers measurement data to machining system efficiently. However, most NCMs need stable environment and low working noise except instantaneous phase-shifting shearing interferometry (IPSSI). Therefore, a new idea about IPSSI is proposed in this paper to realize OMM of lens molds. Unfortunately, it's also difficult to test the high numerical aperture aspheric or free-form lens molds. By comparison, the newly-developed fringe reflection (FR) method is becoming the promising method because it features the high efficiency and high accuracy. However, this method has not been used for OMM system yet. Much research should be conducted for FR OMM technology.

This paper describes the development of a magnetic sensor system for the evaluation of the condition of prestressed strands inside the bottom layer of concrete box beams. The sensor consists of an electromagnet which magnetizes embedded prestressing strand and measures the magnetic field response of the strands using Hall sensors embedded at different positions on the electromagnet. The novel aspect of this comprehensive system is the integration of measuring magnetic flux leakage (MFL) and main magnetic flux (MMF) signals. A computer-aided simulation model has also been developed to use these signals in estimating corrosion. The MFL signal gives indications of the presence of corrosion and cracks or fractures in the strands. The MMF signal quantifies the amount of steel loss in the strands due to corrosion or rusting. Both these techniques have been independently evaluated using magnetic inspection systems which made them suitable to be used in a single sensor system. This comprehensive system was evaluated in a laboratory setting to identify corrosion and strand breaks in prestressing strands. It was observed that the MFL signal could identify the presence of corrosion and strand breaks, while the MMF signal could be used to estimate the loss of steel due to corrosion. This system was also evaluated using it in an inspection of decommissioned prestressed box beams removed from Ohio’s oldest prestressed box-beam bridge. The findings from this inspection revealed a good match with the dissected areas of the box beams. Steps to move the system to implementation are also discussed. With further development improving the accuracy of this inspection system, it can become a valuable tool to bridge engineers for box-beam inspection.

Group-based cryptography is viewed as a modern cryptographic candidate solution to blocking quantum computer attacks, and key exchange protocols on the Internet are one of the primitives to ensure the security of communication. In 2016 Habeeb et al proposed a “textbook” key exchange protocol based on the semidirect product of two groups, which is insecure for use in real-world applications. In this paper, after discarding the unnecessary disguising notion of semidirect product in the protocol, we establish a simplified yet enhanced authenticated key agreement scheme based on cyclic automorphism subgroups of random orders by making hybrid use of certificates and symmetric-key encryption as challenge-and-responses in the public-key setting. Its passive security is formally analyzed, which is relative to the cryptographic hardness assumption of a computational number-theoretic problem. Cryptanalysis of this scheme shows that it is secure against the intruder-in-the-middle attack even in the worst case of compromising the signatures, and provides explicit key confirmation to both parties.

In this paper, a new reference waveform estimation strategy based on an adaptive notch filter (ANF) is proposed for unified power quality conditioner (UPQC). Two coupled ANFs are used to generate the reference waveforms for shunt and series components of UPQC. Mathematical properties of proposed algorithm are presented in detail. The technique is simple and its speed and accuracy are controllable. Moreover, robustness against internal parameter variations is a feature of this method. Numerical simulations result show the superiority of the algorithm for compensation of voltage and current distortions in compare with the conventional methods.

In this paper, the nature and location of hot carrier induced defects is studied for N-channel LDMOS (Laterally Diffused MOS) transistors. These devices are used in wireless base stations and typically operate under high drain bias of 25-30 V, making them highly susceptible to hot carrier injection. In this work, the improvement in hot carrier induced degradation by means of a dummy gate is presented. Using the charge pumping technique, it is demonstrated that, (1) significant electron trapping in the LDD region occurs for devices without a dummy gate in contrast to devices with a dummy gate. (2) For devices with a dummy gate interface traps are preferentially generated in the LDD region.

White LED lamp are gaining a lot of popularity both on the residential and street lighting markets. Those devices are advertised with a very long lifetime compared to conventional incandescent lamps. A measurement campaign including accelerated ageing and stress test is ongoing in Sweden; parts of the data are joined to data obtained in France. The aim of this paper is to report and analyze which factors can be correlated to LED performance changes. A few commercial lamps were bought anonymously in retail stores; each type comprised 12 samples. A first group undergo long-term lumen maintenance test; the second was stressed by frequent switching (50 000 cycles, 30 seconds on/30 second off); the third and the fourth by frequent cycling (3 000 cycles, 30 minutes on/30 minutes off) at 25 °C and 75°C respectively. The assesment are made based on the change of the lumen, lamp efficiency, Correlated Color Temperature and Color Rendering index of the produced light before and after the test.

The calculation of a transformer's parasitics, such as its self capacitance, is fundamental for predicting the frequency behavior of the device, reducing this capacitance value and moreover for more advanced aims of capacitance integration and cancellation. This paper presents a comprehensive procedure for calculating all contributions to the self-capacitance of high-voltage transformers and provides a detailed analysis of the problem, based on a physical approach. The advantages of the analytical formulation of the problem rather than a finite element method analysis are discussed. The approach and formulas presented in this paper can also be used for other wound components rather than just step-up transformers. Finally, analytical and experimental results are presented for three different high-voltage transformer architectures.

The recent introduction of high‐energy storage rings with very long straight sections for dedicated synchrotron radiation research has significantly expanded the parameter space accessible to insertion devices as well. In particular, when the generation of soft x rays on a storage ring such as the Stanford Positron Electron Project (PEP) is considered, its straight sections, which exceed 100 m, may be shown to be naturally amenable to low‐to‐medium K undulators with a large number of relatively long periods. This in turn allows for the establishment of relatively weak on‐axis fields in such devices. In this paper it is shown that these conditions permit the use of electrostatic fields, as well as the concomitant development of fixed‐gap, variable‐period undulators. Such devices are shown to be superior in many respects to the variable‐gap magnetostatic undulators currently in vogue. Two novel variable‐period undulator designs, one for a transverse electrostatic undulator and the other for a helical device (HEU) are described. The performances of both devices are calculated, and the numerous advantages of the HEU configuration in producing either soft or hard x rays of arbitrary polarization on high‐energy rings such as PEP are pointed out.

Wireless Power Transfer (WPT) is a new technology for charging the electric vehicles that can make free humans from annoying wires. In recent years, WPT systems have been developed and have significant advances. Design of an inductive power transfer (IPT) has several sections; the two important of which are design of the power electronic devices and design of the pad topology and electromagnetic issues. In this paper, we have discussed the second section and examined parameters that affect the magnetic coupling coefficient between the two pads especially for DD Pad structure.

High speed transmission of information suffers inevitably by intersymbol interference (ISI) induced by multipath propagation over frequency selective channels. ISI has been a major obstacle preventing the successful implementation of physical layer network coding (PLNC) systems in these environments. Another major obstacle is the high computational complexity of existing algorithms dealing with ISI, which is a determining factor in the design of relay nodes. In this paper, we propose a novel and computationally efficient decision feedback equalizer structure that is utilized at the end node and in conjunction with a simple amplify and forward (AF) technique employed at the relay. We derive the optimal equations for the decision feedback equalizer (DFE) coefficients and evaluate the end-to-end bit error rate performance in frequency selective channels, and provide both analytical and numerical simulation results that demonstrate the feasibility of the proposed approach under realistic channel conditions. The obtained results show that E2E performance is dominated by the channel with most severe frequency selectivity.

A variety of efficient green, yellow, and amber monochromatic phosphor-converted light-emitting diodes (pc-LEDs) were fabricated by simply capping a long-wave pass filter (LWPF) on top of LED packing associated with each corresponding powder phosphor. In this paper, the luminous efficacy and color purity of two green, three yellow, and two amber pc-LEDs were reviewed by comparing the optical properties and current/temperature stability of each LWPF-capped pc-LED. The simple combination of LWPFs and phosphor materials in the pc-LEDs provide a simple means of addressing the low luminous efficacy problem of III-V monochromatic semiconductor LEDs in the various colors of the wavelength range between green and amber (known as the “green gap”). This technique also represents a simple approach to mitigate the sub-linearity problem of the efficacy versus the driving current occurring at a relatively low current in III-V green LEDs (known as “green droop”) to the level of a blue LED. This nano-multilayered filter-capped pc-LED can open further research into developing new color-converting materials (such as powder phosphors, and/or quantum dots) to extend the color palette in the wavelength region of the “green gap” and to improve the efficacy and color purity of color pc-LEDs.

BackgroundRecent advances in mobile technologies have created new opportunities to reach broadly into populations that are vulnerable to health disparities. However, mobile health (mHealth) strategies could paradoxically increase health disparities, if low socioeconomic status individuals lack the technical or literacy skills needed to navigate mHealth programs. ObjectiveThe aim of this study was to determine whether patients from vulnerable populations could successfully navigate and complete an mHealth patient decision aid. MethodsWe analyzed usability data from a randomized controlled trial of an iPad program designed to promote colorectal cancer (CRC) screening. The trial was conducted in six primary care practices and enrolled 450 patients, aged 50-74 years, who were due for CRC screening. The iPad program included a self-survey and randomly displayed either a screening decision aid or a video about diet and exercise. We measured participant ability to complete the program without assistance and participant-rated program usability. ResultsTwo-thirds of the participants (305/450) were members of a vulnerable population (limited health literacy, annual income < US $20,000, or black race). Over 92% (417/450) of the participants rated the program highly on all three usability items (90.8% for vulnerable participants vs 96.6% for nonvulnerable participants, P=.006). Only 6.9% (31/450) of the participants needed some assistance to complete the program. In multivariable logistic regression, being a member of a vulnerable population was not associated with needing assistance. Only older age, less use of text messaging (short message service, SMS), and lack of Internet use predicted needing assistance. ConclusionsIndividuals who are vulnerable to health disparities can successfully use well-designed mHealth programs. Future research should investigate whether mHealth interventions can reduce health disparities.

It is well known that when wood and other vegetable substances are submitted to destructive distillation, there is produced, among other matters, a black dense fluid resembling molasses or common tar. My connection’ with the Ordnance powder-mills having compelled me to examine some of the properties of this substance, which is obtained in large quantities in the process of making charcoal, I was induced to extend my enquiries, in consequence of finding that the nature of the compound has not hitherto been understood. As it is commonly called tar by the workmen, I shall use this term for want of a better. This tar is very inflammable, and so liquid that it may be burnt in a lamp. Although it appears to be an uniform fluid, it contains a great quantity of acetic acid, in a state of loose combination or mixture. For, by washing with water, a great part of this is separated; the water at the same time acquiring a colour from a portion of the tar which is retained in solution by the acid. Boiling water takes up a larger portion, and the tar acquires from this operation a thicker and more pitchy consistence. Lime and the carbonated alkalies separate the acid with ease, carrying away also a portion of the tar which continues united to the solution. With subcarbonate of potash it thus forms in the first instance an uniform solution of a brown colour, but a continuance of trituration or boiling renders it pitchy and

Sir, Since you did me the honour of submitting to the Royal Society my experiments on the comparative light of the Cassegrainian and Gregorian telescopes, I have been so fortunate as to have an opportunity of establishing the conclusions deduced from them by another experiment, the detail of which I trust will not prove unacceptable. The telescopes used on the present occasion were the excellent Gregorian described in my former paper, and a new Cassegrainian constructed by Mr. Crickmore. The diameter of the large speculum of this instrument is 4, 9 inches, the distance between the mirrors only 18 inches, and it bears a power of about 550 (as roughly determined by experiment) with perfect distinctness and considerable light.

Dear Sir, In prosecuting the experiments on the depolarisation of light, which you lately did me the honour to lay before the Royal Society, I have been led to the discovery of a remarkable pro­perty of soft transparent solids, in virtue of which they ex­hibit, by simple pressure, all the optical qualities of doubly polarising crystals. In the paper on depolarisation to which I have now alluded, it has been shown that a mixture of bees' wax and rosin, when melted and cooled between two plates of glass, depolarises a ray which falls upon it at a vertical inci­dence, w'hile the same substance, pressed between two plates of glass, without the aid of heat, produces no effect when the polarised ray falls perpendicularly upon it, but depolarises it at an oblique incidence. In this experiment the crystallization was not produced by pressure, as the unmelted bees' wax was already crystallized; but it is obvious, either that the pressure had modified the natural crystallization of the bees' wax, so as to enable it to depolarise only at an oblique inci­dence, or that its liquefaction between two plates of glass had produced such a change, as to communicate to it the property of perpendicular depolarisation. In whatever manner this difference of action was produced, the effects of pressure seemed to require farther investigation, and in order to be able to apply a sufficient force, without injuring the structure of the substance, I employed animal jellies which could be brought to any degree of tenacity with­out losing their transparency.

In the Philosophical Transactions for 1825, I gave an account of a floating collimator, and added a suggestion for the construction of a vertical floating collimator which had not then been carried into effect. I have since had an instrument of that description made, with such improvements as occasion required, and the results which it has afforded have been so satisfactory that I am induced to lay them before the Society. The collimator which formed the subject of the paper I have mentioned was a horizontal floating collimator. This, in the manner in which I then used it, was the worst form in which the instrument could have been employed; as it was necessary to take the float out of the mercury and replace it in order to complete each observation. The result was therefore liable to be vitiated by any particle of dust or minute bubble of air which might have found a place between the float and the mercury. It cannot therefore but be considered as surprising, that out of one hundred and fifty-one results, only twenty-eight were found in error to an amount exceeding one second, the greatest error being 2".58 and the next 2".

In a paper I had the honour to present to the Royal Society in January last, relative to the construction of achromatic telescopes with fluid lenses, I have stated that between the temperatures of 31° and 84° I had not been able to detect any very sensible change in the index denoting the focal length of the telescope: these observations however being made at intervals of some months, I was doubtful whether there might not be some minute variation which had escaped my notice; and I have since, by means of temperature artificially produced, ascertained that there is a certain small change, and the amount of that change, which is 154/1000ths of an inch in the length of the telescope employed, between each of these extremes and the mean temperature of 57°. That is, the eye-piece of the telescope and the fluid lens being fixed, as was the case in this instrument, the plate lens required an adjustment of 0.134 of an inch, between the temperature of 57° and each of the above extremes, to produce the brightest and most perfect image. Before I proceed, however, to detail the results of my inquiry on these subjects, it will be proper to define a few terms which appear in one or two instances to have been misunderstood.

This paper discusses an optical filter designed using the two-dimensional (2D) photonics crystal. The filter has been designed to work in Dense Wavelength Division Multiplexing (DWDM) communication using ultra cell resonant cavity. The filter analysis was initially carried out by changing the attributes of photonic crystal such as radius of inner ring rods and refractive index. Hence, it is possible to tune the wavelengths with characteristics according to DWDM standard. The filter is designed to work in 1552 nm, 1553 nm, 1554 nm, 1555 nm, 1556 nm, 1557 nm and 1558 nm with 1nm channel spacing and 0.2 nm spectral linewidth, 96 % to 100 % transmission efficiency, and quality factor to be 8000 respectively. The proposed filter was designed and simulated with Finite-Difference Time-Domain (FDTD) algorithms and the results are discussed at the end for the use in Photonic Integrated Circuits.

The same views which the author originally had of the periscopic construction of spectacles, naturally suggested to him a corresponding improvement in the camera obscura. But though it is evident that enlargement of the field of view, and some improvement in the distinctness of images obliquely situated, might be made by causing each part of a lens to be as nearly as may be at right angles to each pencil of rays that are to be collected to a focus, it was not clear to what extent this principle could be carried where the portion of lens is necessarily large, and consequently includes parts that may require a different form for preserving distinctness of other pencils of rays. He has, accordingly, made trial of different forms of meniscus for this purpose, and describes the construction which appears to possess the greatest advantage with least detriment to the brilliancy and distinctness of objects centrally situated. The radii of curvature here preferred are in the proportion of 2 to 1.

The experiments detailed in the present letter were conducted exactly in the same manner as those detailed by Capt. Kater in his former communication, for the purpose of comparing a new Casse­grainian telescope, made by Mr. Crickmore of Ipswich, with the Gregorian used in the former experiments. The diameter of the large speculum in this instrument is 4.9 inches, but was reduced by a ring of pasteboard to 3.6, in order to render the illumination equal to that of the Gregorian, in which the large speculum measured 3.95 inches. The areas exposed to the light being estimated at 7.152 and 10.593, and the magnifying powers at the same time being 157 and 125 respectively, the illuminating powers of the two telescopes are inferred to be as 678 to 290.

When steam is passed through a tube surrounded with water, it is well known that it becomes condensed on the sides of the tube so long as the water continues at a lower temperature than that of the steam; but since the latent heat given out in the condensation of steam soon raises the temperature of the water to 212°, all transfer of heat ceases at that temperature, and the steam then passes un-condensed. But since the temperature at which water may be raised into vapour depends on the pressure of the atmosphere, the temperature of the surrounding water may be kept permanently lower, by removing that pressure, so as permanently to act in condensing the vapour of the first distillation; and being itself raised into vapour by mere transfer of the same original quantity of heat, may be received as an additional product of the same process, by a suitable arrangement of the apparatus. For this purpose, the vessel which serves as condensing worm-tub to the first distillation requires to be fitted with a head and a receiver, all perfectly air-tight; and it may with most convenience be so constructed, that, by application of heat in the first instance to this vessel, the water within may be made to boil completely, so that the air within it will be thereby expelled, and, by a valve or cock, may be prevented from returning when the heat is withdrawn.

On the evening of the 24th of December last, Mr. Howard found the barometer at his house at Tottenham Green at 28·20 inches. The wind was moderate at S. E., the temperature 45°, and water boiled freely at 210°. At 11 p. m. the barometer fell to 27·96 inches, and at 5 a. m. on the 25th to 27·82, below which the author thinks it did not descend. By 8 a. m. it again reached 28. In the twenty-four hours preceding, 0·8 inch rain had fallen, but in the twenty-four hours following there fell none, nor was the wind strong. By midnight on the 25th the quicksilver reached 28·07 inches, and remained there during the twelve hours following,—a thing very rare in our climate. The quicksilver then rose in an uninterrupted curve, and on the 31st touched upon 30 inches, with fine weather. A diagram showing the state of the barometer during the last two months of 1821, as well as the quarter of the wind and quantity of rain fallen, accompanies this paper. During these two months the rain amounted to 10·10 inches, a quantity without precedent in the same space of time at London.

Mr. Ritchie, after a brief exposition of the theoretical views which led him to the construction of his photometer, lays down the fol­lowing as the principles on which it depends:— 1. That radiant heat does not permeate glass. 2. That light is capable of combining with substances which stop it, and expanding them as heat does. 3. That the intensity of light is in the inverse ratio of the squares of the distance.

The apparatus described in this paper (of which a drawing is now laid on the table) is intended to determine the situation of the line of collimation of a telescope attached to an astronomical circle, with respect to the zenith or horizon in some one position of the instru­ment; in other words, to determine the zero point of the divisions on the limb. This is at present usually performed by the use of the level or the plumb line, or by the reflection of an object from the surface of a fluid. The author describes the defects and inconveniencies of each of these methods. Those of the plumb line, when applied to small instruments (to the improvement of which he describes his at­tention to have been particularly directed,) are referrible chiefly to want of sufficient delicacy. Those of the level are referrible to a va­riety of causes not under the command of the observer; while ob­servations, by reflection, the most perfect perhaps of any now prac­tised, require an union of favourable circumstances rarely occurring. Add to these when levels or plumb lines are used, the necessity of reversing the instrument, and observing out of the meridian. And when observations are made by reflection, that of deferring the corresponding observation to the following night, which has proved so great an inconvenience at Greenwich, as to necessitate the erection of a second circle for the purpose of simultaneous observation. The principles on which the floating collimator is constructed are two: the first is the property of a telescope employed by Mr. Gauss, and subsequently by Mr. Bessel, in virtue of which the cross wires of a telescope adjusted to distinct vision on the stars, may be distinctly seen by another telescope, also so adjusted, at whatever distance the telescopes may be placed, provided their axes coincide; the rays diverging from the cross wires of either telescope, emerging parallel from its object-glass, and being therefore refracted by that of the other telescope to its sidereal focus, as if they came from an infinite distance. The author here translates an account by Professor Bessel, of a method of using this principle to determine the horizontal or zenith point of a circle by the use of a level, employed to place the collimating or subsidiary telescope in a horizontal position, a method which though characterized by him as the best mode of using a level that has yet been devised, is still liable to the objections urged against levels in general.

Dr. Brinkley, in this communication, states a number of observations made with the floating collimator of Captain Kater, as applied to the Dublin circle, in which he observes it affords the means of ascertaining the index error with as great precision as by reversion, and that in several points of view it is undoubtedly superior to that method. The reversing principle of the Dublin circle, he observes. Serves very conveniently for a measure of the accuracy of the floating collimator, and serves to show very satisfactorily, that applying this instrument to any circle will introduce no error depending on the collimator itself. The author regards the results of these observations as highly favourable to the principle of the collimator, which he considers as a new astronomical power, and as even belonging to a more advanced era of practical astronomy than the present.

The author begins this paper by an enumeration of the various works on the subject extant in our language, and a general mention of the writings of foreign mathematicians, which he considers as leaving room for further inquiry and simplification. He then states the method employed in his experiments for determining the refractive and relative dispersive powers of his glasses, the former of which is that generally known and practised;—of measuring the radii and focal length of a lens, and thence deriving the refractive index; with some refinements in its practical application, consisting chiefly in using the lens as the object-glass of a telescope, and adapting to it a positive eye-piece and cross-wires, which are brought precisely to the true focus by the criterion of the evanescence of parallax arising from a motion of the eye, as is practised in adjusting the stops of astronomical instruments. The only source of error it involves is in the measurement of radii of the tools which it was found could always be performed within 1/500th of their whole values. The dispersive ratio of two glasses was determined by over-correcting the dispersion of a convex lens of the less dispersive glass by a concave of the greater, and then withdrawing the latter from the former till the achromaticity is perfect, or as nearly so as the materials will admit, and measuring the interval between the lenses and their foci, from which data the ratio of their dispersive powers is easily obtained. The refractive indices and dispersive ratio thus determined, the next step is to find the radii of curvature so as to destroy spherical -aberration. In this investigation, the author does not consider it as necessary to limit the indeterminate problem by any further condition, as others before him have done, but regarding it as a matter of great convenience to avoid contact of the interior surfaces in the centre of the glasses, leaves it open to the optician to make a choice within certain limits, thus avoiding what he considers as an intricate equation arising out of the fourth condition. He proceeds, therefore, to express analytically the aberrations of the glasses, and to deduce the equation expressive of its destruction, which of course involves one indeterminate quantity; this may be either of the radii, or any combination of them. The author chooses the ratio of the radii of the interior and exterior surfaces of his flint lens for this indeterminate, which he assumes, as well as may be, to satisfy the condition of the absence of contact and near equi-curvature of the adjacent surfaces; thence deduces, first, the radii of both of the surfaces of the flint lens; next, its aberration to be corrected; and thence, by the solution of a quadratic, or by the use of a table containing its solutions registered in various states of the data, the ratio of the radii of the convex, whence the radii themselves are easily deduced.

The idea of constructing achromatic telescopes with fluid lenses was first suggested to the author by the attempt of Messrs. Gilbert to apply to practice the principles and rules for the construction of aplanatic object-glasses, laid down by Mr. Herschel in the Philosophical Transactions for 1821. In following these suggestions, the author became sensible of the difficulty of obtaining flint glass of sufficient size and purity for astronomical telescopes; and was thence led to consider the possibility of substituting some fluid in place of flint glass. Dr. Blair had, many years ago, succeeded in making very perfect telescopes of this description, but he still retained the use of flint glass. Among the various fluids adapted to this optical purpose, the author gave a decided preference to the sulphuret of carbon, which combines properties of perfect transparency and freedom from colour, with a refractive index nearly equal to that of flint glass, and with a dispersive power more than double, properties which it appears to retain under all the temperatures to which it is likely to be exposed in an astronomical telescope. After several trials, Mr. Barlow determined the best method of confining this fluid, but was at first unsuccessful in his attempts to construct with it a telescope of 6 inches aperture and 7 feet in length. He afterwards undertook a smaller one of 3 inches aperture, which he at length accomplished, and in the very first trials with it was able to separate a great number of double stars of the class which Sir William Herschel has pointed out as tests of a good 3½-inch refractor. Encouraged by his success, he again attempted a 6-inch object-glass, with a different manner of adjusting and securing the lenses, and considers the result of his endeavour as proving at least the practicability of the construction. This instrument, with a power of 143, shows the small star in Polaris so distinct and brilliant, that its transit might be taken with the utmost certainty; it exhibits distinctly the small stars in α Lyræ, Aldebaran, Rigel, &c. and decidedly separates Castor, γ Leonis, and ϵ Bootis. The belts and double ring of Saturn are well exhibited with a power of 150; and the belts and satellites of Jupiter are tolerably defined with the same power, but will not bear a higher power than about 200. In the usual construction of achromatic telescopes, the two or the three lenses composing the object-glass are brought into immediate contact. But the high dispersive power of the sulphuret of carbon enables Mr. Barlow to place the fluid correcting lens at a distance from the plate object lens equal to half its focal length. By this means the fluid lens, which is the most difficult part of the construction, is reduced to one half or less of the size of the plate lens. This construction, therefore, renders us independent of flint glass, enables us to increase the aperture of the telescope to a considerable extent; and gives us all the light, field, and focal power of a telescope of one and a half time the length of the tube. The author investigates analytically the formulæ for calculating the proper distance of the lenses on this construction, and expresses a hope that further experiments will enable us to determine the precise distance which shall reduce what has been termed the secondary spectrum, inseparable from the ordinary construction, either to zero, or to an inconsiderable amount.

In a paper lately read to the Society, the author stated that he had not perceived any change in the focal length of the telescope, induced by changes of temperature; but he has since ascertained that in order to produce the brightest and most perfect image, the distance of the object-glass requires a minute adjustment, amounting to 0·134 of an inch, corresponding to an elevation of temperature from 57° to 84°, or a depression from 57° to 31°. In order to introduce greater clearness and precision, the author proceeds to define certain terms which he finds it necessary to employ. By the length of the telescope , he would be understood to mean the distance between the object-glass and the focus; by the fluid focus , that between the fluid lens and the focus; and by the focal power of the telescope, he means the focal length of a telescope of the usual construction, which gives the same convergency to the rays, or produces an image of the same size: but he also employs the term focal length of the telescope , as synonymous with the first; that of fluid focal length as synonymous with the second; and that of equivalent focal length as synonymous with the last of these terms.

The author, after noticing the peculiarities discovered by Walsh in the electricity of the Torpedo, and the opinion of Cavendish, that it resembles the action of an electrical battery weakly charged, adverts to the conjecture of Volta, who considered it as similar to that of the galvanic pile. Being on the coast of the Mediterranean in 1814 and 1815, the author, desirous of ascertaining the justness of Volta’s comparison, passed the shocks given by living torpedos through the interrupted circuit made by silver wire through water, but could not perceive the slightest decomposition of that fluid; the same shocks made to pass through a fine silver wire, less than one thousandth of an inch in diameter, did not produce ignition. Volta, to whom the author communicated the results of these experiments, considered the conditions of the organs of the torpedo to be best represented by a pile, of which the fluid substance was a very imperfect conductor, such as honey, and which, though it communicated weak shocks, yet did not decompose water. The author also ascertained that the electrical shocks of the torpedo, even when powerful, produced no sensible effect on an extremely delicate magnetic electrometer. He explains these negative results by supposing that the motion of the electricity in the torpedinal organ is in no measurable time, and wants that continuity of current requisite for the production of magnetic effects.

The principles on which the reflecting, and also the achromatic refracting telescope are constructed, have been recently applied with considerable success to the microscope, and have added much to the power of that instrument. The author speaks with much commendation of the peculiar construction adopted in Mr. Tulley’s compound achromatic microscopes, consisting of a combination of object-glasses of short focus and large aperture, the curvatures of which are such as very nearly to equalize the refractions produced by each. As the magnitude of the aperture, he observes, is valuable only in proportion to that of the pencil of light which it admits, the latter circumstance is that which chiefly claims attention; and as it is often erroneously estimated, a method is pointed out of ascertaining it with sufficient exactness for every practical purpose. He then enters into a detailed description of the several parts of an instrument in his possession constructed on the principles he recommends, referring to the drawings which accompany the paper. The magnifying power may be varied at pleasure, either by drawing out the tubes containing the eye-pieces, or by substituting an eye-glass of different power, or differently combined; and by these changes an uninterrupted range of amplification is obtained from 35 to 800 diameters. No sensible difference as to distinctness is observable, whether the effect is produced by changing the eye-piece, or varying the length of the tubes. The construction of the' instrument admits of the utmost variation of magnifying power without the risk of losing sight of the object viewed : and every part which relates to the illumination being wholly detached from the stage, ample opportunity is afforded of rapidly moving the objects, and bringing into view a succession of them, while the light remains the same. Minute directions are given for the employment of the instrument, and its application to various purposes; and great stress is laid on the importance of a skilful management of the light. In stating the results of his experience on this subject, the author takes occasion to advert to some of the sources of fallacy by which incautious observers with the microscope have so often been greatly misled. When a pencil of rays proceeding from an indefinitely small bright portion of an object is brought to a focus by the most perfect object-glass, the image thus formed is in reality not a point, but a small circle, and will always appear as such if the eye-glass of the microscope be sufficiently powerful. These circles have a considerable analogy to the spurious discs of stars viewed through telescopes. Like the latter, they become much enlarged by diminishing the aperture of the object-glass; and they are also enlarged by increasing the intensity of the illumination. The overlapping of contiguous circles of diffusion has given rise to many fallacious appearances; such as the spottiness which some surfaces assume, and which has been mistaken for globules. This optical illusion has been the basis of some ingenious but visionary speculations on the intimate structure of organic matter. The appearance, in certain directions of the light, of lines on the surface of an object, where they do not really exist, may be traced to a similar cause.

In a paper which I communicated to this Society in 1815, and which was published in the Seventh volume of their Transactions, I described a new species of coloured fringes, produced between two plates of parallel glass. From a consideration of the theory of this class of phenomena, it was obvious that analogous, though much more complicated, systems of rings should be produced between plates with curved surfaces, but it was not till 1822 that I succeeded in detecting them; and so completely are these rings concealed by the superposition of similarly situated images, that, in consequence, of having forgotten my method of observation, I have experienced the greatest difficulty in rediscovering them.My earliest experiments were performed with a double achromatic object-glass, made by Berge, having a diameter of inches, and 30 inches in focal length. The inner surfaces of the crown and flint glass lenses were ground to different radii, as shewn in the section of it at AB, CD, Fig. 5, Plate IX.; and the outer surface of the flint-glass lens was concave, so that there was left between the lenses a meniscus of air A 2, B 3 A.

The great advantage which has attended Mr. Dollond’s ingenious application of the negative achromatic lens to the micrometer eyepiece, seems to make it desirable that the principles on which that lens is constructed, and its general application, should be more fully illustrated than is done in the short extract made from my letter to Mr. Dollond, and given by him in his recent paper in the Philosophical Transactions. In my original fluid telescope, the negative lens was employed for the double purpose of lengthening out the focus and correcting the colour of the front lens; and the great advantage of the lengthening principle was manifested by the high penetrating power of the instrument in the centre of the field. Unfortunately, however, the perfect part of this was very limited, so that when Mr. Dollond constructed the second telescope for the Royal Society, I gave up this advantage for the sake of enlarging the held; but I found that by this means much of the penetrating power of the former telescope was lost; for although I had the same aperture, many small stars which were before very perspicuous were in this instrument seen only with difficulty and under advantageous circumstances of weather, absence of moonlight, &c.

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The principle of the instrument here described is the unequal expansion of different metals by heat. A bar of zinc, alloyed with four or five per cent, of copper, and one of tin, about an inch in breadth, one quarter of an inch thick, and two feet long, is firmly and closely riveted along its face to the face of a similar bar of steel of about one third in thickness. The product of the rigidity and strength should be nearly the same, so that the texture of each may pretty equally resist the strains of flexure. Twelve such compound bars are united in pairs by a hinge joint at each of their ends; having the zinc or alloy bars fronting one another. At ordinary temperatures these bars will be parallel, and nearly in contact; but when heated, they bend outwards, receding from each other at their middle parts, like two bows tied together at their ends. When a more considerable expansion is wanted, a series of such bars is laid one over the other. The movement thus resulting is applied by the author in various ways to regulate the opening of dampers, letting in either cold air or cold water, or closing the draught of a fireplace, as the case may be. He proposes its employment to regulate the safety valves of steam boilers, as working with more certainty than the common expedients.

The Reports received by the Secretaries, from Sir John Herschel, Professor Airy, and Captain Smyth, on the Fluid-lens Telescope constructed for the Royal Society on Mr. Barlow’s principles, were, by direction of His Royal Highness the President and Council, read to the Society at this meeting. Sir John Herschel's Report. I have seen Mr. Barlow’s telescope at Cambridge, and examined it on several objects, in a very fine night, the 25th (if I remember) of June. As I have now no time to give it any further trial at Slough, (where I have no longer, either, any achromatic telescope of sufficient power to compare it with, all my apparatus being dismounted and in course of packing,) I will here state in few words, as my report on it, all I could then collect relative to its action. 1. Achromaticity .—Mr. Barlow’s telescope is remarkably free from the dispersion of colour, very much more so than I could have expected from the nature of the correcting medium, and nearly or quite as much as could be desired.

The application of a concave achromatic lens to the wired micrometer of a telescope, arose out of the series of trials that were made for the purpose of correcting the aberrations of the eye-glasses applied to the telescope constructed by the author for the Royal Society, with a fluid-correcting lens, on the plan suggested by Professor Barlow. The concave lens, being interposed between the object-glass and the eye-glass, and being at the same time achromatic, combines the advantages of doubling the magnifying power, without a corresponding diminution of light, and without altering the apparent distances of the threads of the micrometer. The results of the trials made with telescopes to which this addition was made, are given in a letter to the author from the Rev. W. R. Dawes, of Ormskirk; from which it appears that Mr. Dollond’s method was attended with complete success. Mr. Dawes states, that, in order to put its illuminating power to a severe test, he had examined with this instrument the satellites of Saturn and the minute companion of k Geminorum, but could discover no decided difference in the apparent brightness of the former, allowance being made for the difference in the power employed; and the latter star was seen quite as distinctly with a much smaller power. Extracts are subjoined from a letter of Professor Barlow’s to the author, containing formulæ for the construction of the lens.

Respecting the air in question, which Dr. Davy had found to consist of about 80 per cent, of azote and 10 oxygen, he had remarked that two views might be taken of its origin; the one, that it was of volcanic source; the other, that it was derived from the sea water, and merely disengaged by the heat of the volcano. Dr. Davy, rejecting the former of these views, had adopted the latter, for reasons, the validity of which was controverted by Dr. Daubeny; and the purpose of the present paper is to answer the objections urged against them, and to bring additional evidence in support of his opinion.

The first part of this paper is occupied by an investigation of the circumstances attending the fœtal development of the Torpedo. In the first stage of embryonic growth which the author had an oppor­tunity of observing, when the embryo was about seven tenths of an inch in length, it had neither fins nor electrical organs, nor any ap­pearance of eyes; it exhibited short external branchial filaments, not yet carrying red blood; and there was a red spot in the situation of the heart, communicating by red vessels in the umbilical cord with the vascular part of the egg. There is no membrane investing the fœtus, as is the case with some species of Squall ; nor any fluid in the uterine cavity; neither could the author find any urea or Iithic acid in that cavity. By taking the mean of many observations, it appeared that the weight of the egg, before any appearance of the embryo, is 182 grs., and after its appearance, including the weight of the latter, 177 grs.; while the weight of the mature fish is about 479 grs.; showing an augmentation of more than double. Thus it differs remarkably, in this respect, from the fœtal chick, which at its full time weighs consider­ably less than the original yolk and white from which it is formed. No communication can be traced between the fœtus of the Torpedo and the parent, through the medium of any vascular or celiular structure; and the stomach of the former is always found empty. Hence the only apparent source of nourishment is absorption from the surface; and the author states his reasons for believing that the branchial fila­ments are the principal absorbing organs, the materials they receive being chiefly employed in the construction of the electrical organs, while those which enter into the composition of the body generally are absorbed by the general surface of the fœtus. The author is led, from his researches, to the conclusion that the mode of reproduction in the Torpedo is intermediate between the viviparous and the ovoviviparous. In the second part of the paper, the author discusses the question as to the number of species of the genus Torpedo existing in the Mediterranean; and concludes that there are only two, viz. the Ochiatella and the Tremola .

Dr. Davy complains that Mr. Faraday has, in the paper referred to, made certain statements with respect to the opinions of Sir Humphry Davy relative to the conducting powers of dry nitre, and caustic potash and soda, when in fusion by heat, and also with regard to other matters connected with voltaic electricity, wdiich are not correct; and vindicates Sir Humphry Davy from the charge of want of perspicuity in the statement of his views of these subjects. A Note by Mr. Faraday on the preceding Remarks by Dr. Davy was then read, in which he replies to the charges there brought forward, and justifies those statements, the accuracy of which had been impugned by Dr. Davy.

The method employed by the author for obtaining, by a combination of lenses, the convergence to foci of the colorific solar rays, together with the dispersion of the calorific rays, consists in making a beam of solar light, which contains both kinds of rays, pass, after it has been converged to a focus by a convex condensing lens, through a second convex lens, placed at a certain distance beyond that focus: that distance being so adjusted as that the calorific rays, which, from their smaller refrangibility, are collected into a focus more remote from the first lens than the colorific rays, and consequently nearer to the second lens, shall, on emerging from the latter, be either parallel or divergent; while the colorific rays, which, being more refrangible, had been collected into a focus nearer to the first lens, and more distant from the second, will be rendered convergent by this second lens; so that the second focus, into which they are thus collected, will exhibit a brilliant light without manifesting any sensible degree of heat. The light so obtained may be advantageously applied to the solar, and to the oxy-hydrogen microscopes, from its producing no injurious effects on objects inclosed in Canada balsam, or even on living animalcules exposed to its influence. Another improvement in the construction of the microscope employed by the author, consists in the cell for holding objects being made to move quite independently of the field glass; so that the best focus is obtained by an adjustment which does not disturb the field of view.

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In this paper, a 64 mm×64 mm matrix polymer solar cell (PSC) was fabricated by air-brush spray deposition. Although the open-circuit voltage (Voc) and the fill factor (FF) both need to be improved, the efficiency of matrix PSCs still reaches about 1.82%, and especially the current density achieves nearly 20 mA/cm2. The results verify that air-brush spray deposition is a suitable method to prepare large area PSC devices, and the process we use in this paper can be easily transplanted to roll-to-roll production.

Multi-level AC-AC converter has the advantages of reducing switch voltage stress, adapting to high voltage input and reducing waveform distortion. In this paper, a symmetrical switched capacitor multi-level (SSCML) AC-AC converter is studied. The switched capacitor (SC) technology is introduced into the AC-AC converter, which has the advantages of small size, high efficiency and high power density. Firstly, the topology of SSCML AC-AC converter and its control strategy are introduced. Then, the working principle of the topology is analyzed, and the relationship between input voltage and output voltage is derived in detail, as well as the expression of switch voltage stress. Finally, a 300W prototype is built to verify the proportional relationship between input voltage and output voltage. The prototype and experimental results prove that the multi-level AC-AC converter using SC technology has the advantages of small size and low voltage stress. The experimental results also prove that the voltage stress is proportional to the modulation ratio, which is the key to reducing the voltage stress.

The Rev. Dr. Scoresby, after a few introductory observations, remarked that he might have occasion to refer very briefly to the principle of the instrument as necessary to the illustration of his subject. For the information of those who might not be aware of the construction of the telescope, he would observe that the principle upon which it acted was this, —it simply depended upon the property of a convex glass and of concave reflectors, which produce an image at their focus. For instance, if he had a magnifying glass, and admitted the light through that, more particularly in the way of the camera obscura, there would be an image of the object formed at the other end. That image would be in proportion to the focal length of the glass, so that the telescope which had the longest focal distance would magnify the best. It is the area or surface of the glass, or the metal, which gives the quantity of light, but a speculum of one-inch size will produce the same magnifying power if the focal length is fifty-four feet, as the six feet telescope of Lord Rosse. The only other thing with reference to the principle was the examination of the object, which can be shown by a simple experiment with a lantern or candle. If, for instance, he placed a magnifying glass near a candle or a lamp, he would have thrown on a piece of paper the image of the candle inverted. The forms of ...

In this communication the author describes a series of experiments, made for the purpose of determining the distribution of the voltaic force from its source in the generating metal, as indicated by the de­position of reduced copper in the constant battery; and, considering that the voltaic combination most perfect in theory would be one formed by a solid sphere, or point, of the generating metal, sur­rounded by a hollow sphere of the conducting metal, with an inter­vening liquid electrolyte, he constructed an apparatus making as near an approximation as possible to these conditions. It consisted of two hollow brass hemispheres, applied to each other by exterior flanges, and rendered water-tight by an intervening collar of leather. In the centre of the hollow sphere thus formed, a ball of amalgamated zinc was suspended by a well-varnished copper wire, connected with one of the cups of a galvanometer, and was contained in a mem­branous bag holding the acid solution ; the whole being introduced through a short tube in the top of the upper hemisphere, and the remaining space being filled with a saturated solution of sulphate of copper. The galvanic circuit was completed by wires establishing connexions between either hemisphere and the other cup of the galva­nometer. For measuring the forces developed, sometimes the ordi­nary magnetic, but in the greater number of instances the calorific galvanometer of De la Rive was employed; the indications given by these instruments were noted, on the completion of the circuit, in various ways; and the deposition of copper in the hemispheres was examined after the apparatus had been in action for a certain number of hours. The following are the conclusions which the author deduced from a series of experiments thus conducted: 1st. The force emanating from the active zinc centre diffuses itself over every part of the upper hemisphere, from which there is a good conducting passage for its circulation.

In the instrument here described, there is provided, in addition to the ordinary barometric tube (inverted, in the usual way, in a cistern of mercury,) a second tube of the same dimensions, placed by the side of the former, and likewise filled with mercury, but only to the height of twenty-eight inches above the level of the mercury of the cistern. This tube is closed at its lower end, and fixed to a float supported by the mercury in the cistern: and it bears, at its upper end, an ivory scale, three inches in length. The elevation of the mercury in the barometric tube is estimated by the difference between its level and that of the mercury in the closed tube; and is measured on the ivory scale by the aid of a horizontal index, embracing both the tubes, and sliding vertically along them. As the float which bears the closed tube, to which the scale is attached, rests freely on the mercury in the cistern, and consequently always adjusts itself to the level of that fluid, no correction for the zero point is needed; and as every change of temperature must similarly affect the columns of mercury in both the tubes, after the scale has been adjusted so as to read correctly at any given temperature, such as 32°, which may be effected by comparison with a standard barometer, every other reading will correspond to the same temperature, and will require no correction. The author considers the error arising from the difference of expansion corresponding to the different lengths of the two columns of mercury, and which will rarely amount to one four-hundredth of an inch, as too small to deserve attention in practice, being, in fact, far within the limits of error in ordinary observations. Subjoined to the above paper is a letter from the author to Sir John Herschel, containing a statement of comparative observations made with a mountain barometer, and with the compensation barometer, from which it appears that the use of the latter is attended with the saving of a great quantity of troublesome calculation. The comparative observations are given in a table, exhibiting a range of differences from +˙012 to -˙016 of an inch.

The author observes, that experience has shown it to be impracticable to make a telescope even approach to achromatism, by employing the same object-glass with an astronomical, as with a terrestrial eye-piece: for if the focus of the blue rays from the object-glass be thrown forwards, as it must be in order to make it impinge upon the focus of the blue rays of the terrestrial eye-glass, then there will be produced a great over-covrection for the astronomical eye-glass; and vice versa . Hence it appears that the application of Huyghenian eye-pieces to refracting telescopes, is incompatible with the conditions of achromatism, throughout the entire range of magnifying power; and that in reflecting telescopes they unavoidably introduce dispersion, because they are not in themselves achromatic. These defects the author proposes wholly to obviate, by substituting for the Huyghenian eye-pieces, single achromatic lenses of corresponding magnifying power; consisting of the well-known combination of the crown-lens, and its correcting flint-lens, having their adjacent surfaces cemented together; thus avoiding internal reflections, and enabling them to act as a single lens. The achromatic eye-pieces which he uses were made by Messrs. Tulley and Ross, and are of the description usually termed single cemented triples .

The author’s attention having been long directed to the remarkable fact, that odour, resembling that of phosphorus, is given off during the escape of positive electricity from the point of a conductor into air; and is likewise perceptible when lightning has struck any object, and also when water is electrolyzed, he has investigated the circumstances attending these phenomena; and the results he has obtained will, he expects, afford a clue to the discovery of their cause. The odour which accompanies the electrolyzation of water, he observes, is only disengaged at the positive electrode. He also finds that the odoriferous principle can be preserved in well-closed glass bottles for any length of time. The only metals which yield this odour are gold and platina; but dilute sulphuric, phosphoric, and nitric acids, and from aqueous solutions of several of the salts, also disengage it. Raising the temperature of the fluid to the boiling point prevents the odour from arising; and the addition of comparatively small quantities of powdered charcoal, iron, zinc, tin, lead, antimony, bismuth or arsenic, or of a few drops of mercury, to the odorous principle contained in a bottle, immediately destroys the smell; and the same happens when platina or gold, heated red hot, is introduced into the vessel containing that volatile substance.

The experiments described in this paper were made on a single fish, of middle size, recently taken out of the water. Portions of the electrical organs, cut transversely in thin slices, exhibited under the microscope many elliptical particles, apparently blood-corpuscles, the long diameter of which was about 1-800th, and the short about 1-1000th of an inch, and a few filaments, apparently nervous, irregularly scattered; some of them tortuous, and all about the 2000th of an inch in diameter. The latter bore no resemblance to muscular fibres. The blood contained some globular particles, having a diameter of the 4000th of an inch, mixed with the elliptical. The mucus for lubricating the surface was found to contain globules apparently homogeneous in substance, but of irregular outline, and in size varying from the 2000th to the 270th of an inch.