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During a period of high pollution in December 1962 smoke samples were taken on Whatman cellulose fibre paper and on glass fibre paper, and the weight collected on the latter was used to derive a calibration curve for the standard filter-paper method of estimation of smoke. While the samples from which the calibration was derived were being collected the nature of the pollution changed very little, but qualitative changes in pollution may result from altered weather conditions and the errors which this introduces are considered. The effects which the texture of the paper and the colour and overlapping of the particles may have on the measured reflectance are also discussed.

Reflection factor curves for gaslight photographic papers with matt and glossy surfaces have been obtained for a fixed direction of view of 30°, this direction lying in the plane of incidence. The papers give not only a specular peak, but also a "throwback" peak whose maximum occurs when the directions of incidence and view coincide. The height of the throwback peak is related to the reflection factor of the paper at the angle of the throwback peak by a linear law. By considering in turn the different components of the photographic paper, the throwback peak has been shown to have its origin in the baryta layer. The complete reflection factor surfaces for a fixed direction of view of 30° have been built up for two pieces of matt surface paper from the reflection factor curves in different planes. As various liquid suspensions also give a throwback peak, the peak may have its origin in some kind of scattering effect.

Pressure pulses of 8.2 × 107 dyn cm-2, each lasting for about 0.01 sec, were applied to paper, and the scattered light from it was measured simultaneously in order to study the response of pores in paper under dynamic conditions. During the compression phase the deformation in pore surface, i.e. the loss in fibre-air interface, is found to be linearly related to the square root of pressure, and the minimum pressure required to compress a paper to the non-porous state is estimated to be around 5 × 108 dyn cm-2, depending on the type of paper. The decompression curve, however, always follows a different path; thus, a cycle of compression and decompression shows large hysteresis. An approximate calculation is made of the energy loss per cycle, and this shows the associated temperature rise to be less than 1 degc. The delayed recovery from compression is large compared with the elastic recovery, but the permanent set is very small. Both the resistance of pores to compression and the energy loss per unit volume seem to be related to the paper density.

A new technique for measuring peak pressures of repeated high amplitude sound pulses in liquids is described. The method involves the transfer of carbon from carbon paper to white `printing-out paper' as a result of the pressure exerted by a pulse. The darkening produced on the white paper was estimated photometrically and used as a measure of the peak pressure in the pulse. Using this procedure, measurements were made in a water column of pulse peak pressures up to 700 atm.

A device for scanning electrophoresis and chromatography paper strips is described. A pen recorder traces the curves of the optical density, integral of the optical density, radioactivity intensity and integral of the radioactivity intensity as a function of position of the paper strip. The scanning is carried out automatically.

Deposits of coal dust collected on filter paper from airborne clouds have been studied in connexion with their light screening power. This depends on the nature of the paper as well as the size and concentration of the particles. Nine kinds of paper were investigated, two of them in detail. Some idea has been obtained of the qualities necessary in a filter paper in order that the dust deposits will have maximum optical density. Theoretical expressions are derived for light screening according to how the particles are dispersed in the paper. Maximum screening would result if each particle shadowed individually, but this is only possible in very sparse deposits; otherwise, overlapping of the particles has to be allowed for. Diffraction of light by the particles and the effects of diffusion of light in the paper are discussed.

The device will produce a graph from data in the form of five-track paper tape. The rate of plotting is 20 points per minute at an accuracy of up to one part in 1000. Apart from a standard ten-millivolt potentiometric recorder and tape reader, the device requires 21 transistors, 2 valves and 22 relays.

The paper deals with a problem which can occur with high speed paper tape readers. It describes the effects resulting from the generation of static electricity and experimental means used in measuring the charge. Various methods of controlling the charge are described and the effects of humidity upon the conductivity of paper are studied.

Work done during the past twenty years on the physics of fibre bonds in paper and the behaviour of paper under mechanical strain is reviewed. The first major section of the article illustrates the chemical nature of the cohesion in paper and reports the results of direct observations on fibre-to-fibre bonds. A statistical theory of the geometry of fibrous networks is shown to be a basis for the characterization of fibre bonding in paper. The second major section is concerned with the mechanical behaviour of paper. This is shown to be a complex subject because paper exhibits almost every known rheological property. Direct, conventional rheological methods, molecular theories and the concept of elastic networks are discussed in this context. Further complications arise from any changes in the water content of the environment. Such effects are conveniently thought of as a competitive process wherein cellulose and water compete for hydrogen bonds for their hydroxyl groups. Not least among the rheological phenomena that paper exhibits is mechanical fracture. This is a discontinuous process that is found to be intimately connected with the mechanical work done on the specimen and is principally governed by its geometrical distortion.

Experience in this laboratory of high-speed paper tape punches (Tally Model P-120), connected as the output of a computer (Ferranti Argus 500), has shown that punching errors arising from a mechanical origin are frequent. If the tape supply is arranged to be `drag free', these errors are almost eliminated, thus avoiding costly waste of operator and computer time. This note describes a prototype of a high speed tape supply device which was designed for use with an 8 hole 120 character per second paper tape punch. The device is simple and inexpensive to construct, and has proved reliable in use.

A simple inexpensive device is described, which tensions and spools the punched paper tape emerging from teleprinters. It is effective in overcoming the 'bunching' of the punched tape which can occur immediately before the tape punching mechanism.

An automatically recording densitometer is described depending on the use of a photomultiplier operated at constant anode current. The application of this instrument to evaluation of electrophoresis data from filter paper strips is discussed. Some advantages of the circuit are outlined.

A new descriptive formalism is introduced to represent the state of a bonded random network of fibres, such as paper, when subjected to mechanical deformation. Energy is considered to be distributed among the lengths of free fibre between inter-fibre bonds and a criterion for the fracture of these bonds is postulated. The theory is used in the present paper to derive the cumulative fracture of bonds as a function of time in a network which suffers a uniform rate of elongation. Good agreement was obtained with experimental recordings of the failure of bonds in a thin sheet of paper. No systematic influence of the rate of straining on the mode of bond failure was detected.

No corrections are made in Mr Hampton's results, and it is shown that they are based on sound reasoning. The dimensional requirements are straightened out, however, and, together with the theoretical justification of the Adams and Williamson formula for the fundamental law of annealing (see previous paper), this seems to put the theory of the annealing process on a fairly sound basis, and to justify in every way the practical conclusions of Mr Hampton's paper.

The method of plotting observations on probability paper becomes clear when the curve on probability paper is regarded as an integral of the histogram. The observations are divided into intervals, which may often conveniently be the natural interval of measurement, and the total frequency of observations up to and including the nth interval is plotted against the upper end of the nth interval. It is shown that in drawing a straight line to fit the observations, less weight should be attributed to deviations from the line towards its ends than in the middle regions.

The Paper is the fourth of a series dealing with the subject of Cohesion. The aim of the present Paper is to consider the value of molecular force as indicated by Van der Waals gas formula (particularly at the critical state where the liquid and gaseous states merge), and to relate the results to the previous enquiry.

The Barkas analysis is applied to a series of nine papers of known visual gloss. With some reservations, the analysis is found to hold approximately and the distribution of mirror facets so derived is found to accord well with the surface structure of the papers as found by microscopic examination. It is concluded that, whilst the analysis is of negligible value for practical gloss determinations, it appears to present a useful method of investigating the surface structure and "finish" of paper and similar delicate materials. The gloss of the papers examined appears to be assessed solely by the intensity of the light reflected at the specular angle and not by the contrast noted by examination at different angles nor by the ratio of specularly-reflected to diffusely-reflected light. Some suggestions for future research are given.

It is established that when a uniform film of liquid is pressed against the surface of a material through rolling, the depth of the deepest part of surface which can be coated is equal to the initial thickness of the film. The total coated area, which may be determined by the change in diffuse reflectance of the material, varies with film thickness but is shown to be independent of the rheological properties of the liquid. These observations are utilized in a treatment developed to determine the topographical structure of a surface. Results show that the surface structure of paper can be described by the Gaussian distribution of the logarithm of depression. The surface structure is sensitive to both load and velocity of rolling, but tends to become stabilized at high load or low velocity. It is suggested that the maximum of the pressure distribution in rolling matters most, but its effect may be complicated by the varying number of stress-bearing sites on the surface and by the interaction between them and their neighbours. The effect of velocity is attributed primarily to the viscoelastic nature of paper and secondarily to the number of stress-bearing sites.

A recent paper on time measurement by L. M. Stephenson (ibid., vol. 3, 368, 1970) is examined in detail. It is argued that the paper sheds no new light on the subject and that it is altogether misleading. In particular, while the notion of a primary time scale in special relativity bears some relation to certain elements that are familiar and valid. Stephenson's own treatment of the notion appears to be wholly erroneous.

When ink is applied to a paper surface from a smooth plate the area which becomes coated is well known to depend on the thickness of the ink film on the plate. A simple, two-parameter relation has been found which describes this dependence, and it has been shown that this effect provides a convenient method of determining the topography of the surface of a paper. A treatment has been developed whereby the frequency distribution of the depth of depression in a paper surface can be determined by measuring the areas covered with ink when films of different thicknesses are applied. The area coated may be measured directly or found by observation of the diffuse reflectance of the printed paper: an equation is derived whereby the distribution of depression can be calculated to a reasonable accuracy from measurements of the diffuse reflectance. Typical distribution curves obtained by this method show maxima near the shallow end - at about 0.2 μm for coated papers and at about 1 μm for newspapers.

Since the Thomas Young Oration of 1923 was delivered a number of important papers dealing with the history of spectacles have been published. The present article gives a summary of the fresh evidence brought forward in these papers.

Examination of recent papers on dimensions and physical quantities suggests a need for more careful definition of these quantities. This matter was dealt with in an earlier paper, but is now expanded and treated in more detail. It is maintained that if definitions were more precise there would not be the same confusion about the dimensions of certain quantities. There may still be differences of opinion on the most appropriate definition of a particular quantity, but if the definition is adequate then there is no doubt about the dimensions of the quantity as deduced from the definition. In this connection there is discussed the use of quantities defined as ratios, such as specific gravity (or relative density), and their more fundamental equivalents, such as density. Further, a logical set of definitions leads to the conclusion that the introduction of certain universal constants is unnecessary - for example, the Newtonian constant N in the equation for force, F=Nmf. Finally, there is discussed briefly the definition of the intensive quantity, temperature, in terms of the extensive quantity, energy.

A form of reflectometer for measuring the show through tendencies of printing papers is described. Its grading of a series of nineteen papers covering a wide range of opacity is in good agreement with the judgment of 173 trade observers. The instrument can also be used for measuring reflexion factors. Diffuse illumination, normal viewing and normal illumination, diffuse viewing can both be used and are shown experimentally to be practically equivalent, but the latter is more convenient. The opacity figures can be converted to the U.S. TAPPI Opacities by means of an equation due to Judd: the results obtained are in good agreement with measurements made on the American Bausch and Lomb Opacimeter.

Different kinds of writing have different missions. In scientific writing the principal objective is to convey information. This paper examines several of the essential characteristics of effective scientific expositions, identifies and discusses certain steps the author should take before actually beginning to write, and considers the separate sections of a typical scientific paper or report from three viewpoints - nature of content, sequence of preparation, and pattern of presentation.

The performance of the Bausch and Lomb and Sheen glossmeters is examined. Comparison of gradings of nine printing papers according to visual and instrumental means shows that, despite high correlation between them, there are nevertheless important discrepancies not attributable to sampling, instrumental or personal errors. The effect of angle of incidence and viewing on grading is investigated; best results are noted at 45°, and the discrepancies become more pronounced at greater angles. Gradings of the same papers according to the Jones, Askania, Goerz, Ostwald and Klughardt methods are examined; all are found unsatisfactory. It is concluded that, for the limited range of papers tested, the most satisfactory grading is given by measurements of the intensity of light received when angles of incidence and viewing are 45°.

For a range of papers of luminance factor varying from 20% upwards and of gloss varying from almost complete matt to gloss high enough to give fair mirror images the equation G = S(a + 10/L) is proposed, where G is a measure of visual gloss, S is the relative intensity of reflected light under 45° - 45° conditions of illuminating and viewing, L is the luminance factor expressed as a percentage and a is a constant which, under the conditions used by the authors, is approximately 0.20. The visual gradings of eight papers out of ten are not markedly affected by the conditions of observation, but for the remaining two there is a highly significant shift in grading according to whether these conditions permit formation of mirror images or not. Gloss is considered to be a gestalt, corresponding to no single physical property of a surface, being judged by appraisal of a physical situation taken as a whole. The validity of the method used in establishing the psychological gloss scale is checked by experiments in weight grading.

An apparatus is described for measuring the mechanical condition of paper It was primarily designed for the estimation of the extent of the deterioration that had taken place in the paper dielectric of an electric cable under various conditions of use. The principle of the method consists in measuring the energy required to tear through a small strip of the sample. The tear is made by a wire of specified size actuated by a falling weight, and the paper is held in a special form of clamp.

A method is described for making a projection drawing from any point of view in which the drawing is set out directly from the dimensions of the object without the use of intermediate plans and elevations. Seven key figures are given with the necessary numerical factors which give directly the proportions for forty-two points of view. By the use of square ruled paper and these figures, aided by the slide rule, figures may be drawn in which the dimensions are found by means of the rulings on the paper only, so that scales of length are not needed. An example of the use of the method is an illustration of two pentagonal dodecahedrons, one that of Euclid and the other that of a crystal of iron pyrites. The last part of the paper deals with the solution of the spherical triangles on which the method depends.

An analogue technique is described giving good approximate solutions of the biharmonic equation. The method uses two plane sheets of conducting paper linked by an array of resistors. The technique is applied to problems involving the slow flow of a viscous fluid past uniformly spaced parallel fibres. Calculated values of the Kozeny constant from the results show much better agreement with the practical and theoretical values than those derived from previous analogue solutions.

A review has been made of the previous attempts to formulate a theory for the elastic modulus of paper in terms of fibre properties. The suggestion is made that, by considering the case of uniaxial stress, previous authors have attempted a problem that is too complex for the present state of knowledge. It is suggested that the case of equal biaxial strain is theoretically simpler and that verification of such a theory can be made more reliably. The biaxial theory is developed and the elastic modulus is written in terms of the moduli of the fibres and the bonded area of the sheet. The biaxial modulus has been measured for three levels of fibre bonded area for one pulp and these admittedly sparse data are in agreement with the theory.

In connexion with Mr Connolly's paper on "New Types of Levelling Instruments with Reversible Levels" it is shown how an accurate test of reversible levels can be carried out in a simple manner. It is also pointed out that levelling instruments with reversible levels have been constructed in Germany since 1875.

The paper cited in the title by Winkler, Hall, and Percival (WHP) documents some important aspects of the widely referenced United States Naval Observatory (USNO) Time Scale system. We augment the text of WHP regarding the mutual synchronization to within 5 μs of the Time Scale, UTC(USNO), with another widely referenced time scale, the National Bureau of Standard UTC(NBS) Time Scale. We show that some of the information available to WHP can be utilized to give even more precision to the USNO Time Scale system and that some of that information has been improperly interpreted causing some errors by WHP in their conclusions regarding time scale precision, clock weighting factors, and drift in rate of the time scale.

An analysis is made of the effect of orientation of the fibres on the stiffness and strength of paper and other fibrous materials. It is shown that these effects may be represented completely by the first few coefficients of the distribution function for the fibres in respect of orientation, the first three Fourier coefficients for a planar matrix and the first fifteen spherical harmonics for a solid medium. For the planar case it is shown that all possible types of elastic behaviour may be represented by composition of four sets of parallel fibres in appropriate ratios. The means of transfer of load from fibre to fibre are considered and it is concluded that the effect of short fibres may be represented merely by use of a reduced value for their modulus of elasticity. The results of the analysis are applied to certain samples of resin bonded fibrous filled materials and moderately good agreement with experimental results is found.

The addition of resin to paraffin wax used for paper condenser impregnation gave no improvement in the temperature coefficient, but produced a temporary "reflex" phenomenon in the dielectric losses during temperature changes.

A method of deducing Young's modulus of isotropic materials from flexural resonant frequencies which was suggested in a recent paper by D. Hardie and R. N. Parkins may lead to errors of up to 10%. The use of tabulated correction factors is shown to be a more satisfactory method of treating the experimental results, leading to values accurate to better than ½%.

It is shown that in a recent paper by Chaudhuri and Ganguly entitled Absorption and Fluorescence Spectra of Crystalline trans- stilbene (see ibid., 1969, 1560), the crystalline samples were not sufficiently thin to obtain accurate absorption spectra. Direct absorption and specular reflection spectra are presented and the large deviation from the oriented gas model cited by Chaudhuri and Ganguly is shown to be primarily a manifestation of experimental difficulties.

Current flow analogues are widely used to realize pictorially the concept of a 'field'. Such analogues can be highly complicated in practice but all the principles involved can be demonstrated clearly in, and useful results gained from, the conducting-paper version.

A conducting paper analogue has been employed to provide a rapid and inexpensive method for the determination of values of stress in fields of uniaxial tension and of pure torsion, to which the equations of Laplace and Poisson apply. The reliability of the equipment has been verified by comparison of selected experimental results with those of known theories. Applications of the technique to the determination of the stress distributions in thin sheets containing geometric openings are given, and also to the determination of the stress distribution in a circular shaft containing a keyway, in pure torsion. The relevance of of Inglis' theory for equivalent elliptic holes is examined. Results are presented in graphical form.

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An iterative method of tracing rays through an optical system which is suitable for operation by a fully automatic recording machine is described. The rays may be axial or skew, and the surfaces of any rotationally symmetrical form suitable for optical working. The relation of this method to earlier schemes and the advantages to be gained by successive approximations are considered.

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