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A lattice model for the aether is shown to give indications of a fundamental charged particle of massM such thatM/me =3/4(108)3π2(1843)−4/3[(3/2)1/2 − 1]−1 =1836.15232, a value very close to the observed proton-electron mass ratio of 1836.15152(70).

The transverse aether drag experiment of Jones (1972, 1975) is explained by calculating the effect of the moving glass disk on the lateral diffraction spectra of the index gratings used to detect the lateral displacements. Although the undiffracted light is moving perpendicularly to the transverse motion of the disk, the lateral spectra are not, and are therefore subject to longitudinal effects due to a small component of the disk motion. The result of Landsberg (1961) can therefore be applied, giving a dispersion term in the formula for lateral shift.

There are several differences between the theories of matter published by Rene Descartes in I637 and I644 which deserve attention. The differences follow from Descartes's well-known identification of substance with spatial extension, and his consequent rejection of the void. Since there was no void space, Descartes argued, a very finely divided subtle matter must extend throughout the universe in order to fill all space not otherwise occupied by the less finely divided ordinary matter.' In the I637 treatises La dioptrique and Les meteores Descartes described only one kind of subtle matter, the primary function of which was to transmit the action of light. Yet when he came to write Principia philosophiae (I644), he believed that the subtle matter was divided into two separate elements. One of these remained an aether for light transmission, but the other had lost this property and was believed instead to be active in magnetic effects and in the electrification of glass, and to form part of the substance of flame. The transition from one subtle matter to two more complex forms might seem a quite straightforward development in Descartes's thought were it not for the existence of another treatise, supposedly the earliest of all, Le monde, in which two subtle matters were postulated. Le monde was first published posthumously in I664. But it has generally been supposed that the version published then was one Descartes had prepared between I629 and i633.2 When Galileo was accused of heresy in asserting the motion of the earth, Descartes decided not to publish his own views at that time, but he did not give up hope that Le monde might appear eventually. Between I633 and I640 his letters to Marin Mersenne contained many references to 'mon Monde', particularly when he did not want to explain any details of physics that depended on a knowledge of its contents. Like everyone else, Mersenne would have to await its publication before he could hope for clarification. In opposition to the commonly accepted view, I should like to argue

Special interest attaches to Newton's work in optics, since it was the investigation he first considered complete. When he was appointed to the Lucasian chair in I669, he chose the theory of colors for his initial series of lectures, and with a paper drawn from the lectures he presented himself before the scientific community. As the contents of the Portsmouth Papers have become known, moreover, it has proved possible to follow Newton's steps as he developed the theory of colors, from the first suggestion jotted down in a student notebook, probably in 1664, that colors are produced by the analysis of white light, through the systematic essay 'Of Colours' from about I666, to the first series of lectures early in 1670.1 Although the essay 'Of Colours' contains a number of experiments expressing the fundamental conceptions on which his analysis of colors in thin plates rested, experiments which were later elaborated into Book II of the Opticks, most of the early MSS. have seemed to point primarily toward Book I. When he prepared the Lectiones Opticae, he confined their treatment of colors to the material that later went into Book I, and the paper sent to the Royal Society in 1672 covered the same ground in a briefer form. Only in 1675 did the 'Discourse of Observations' bring forward what was to be Book II. Its content has seemed to spring across a gap of nearly ten years, and except for the original suggestions of H00KE and the brief descriptions of I666 it has appeared to arrive at maturity without having had to grow up. On the face of it this was an improbable situation. Newton's basic idea, that colors arise from the analysis of white light rather than from its modification, had from the beginning demanded an explanation of more than the prismatic spectrum. If the concept of analysis were to be viable, it had also to explain the colors of solid bodies, which is exactly what he intended the experiments with thin films to do. Not only refraction, but reflection as well, could analyze the heterogeneous mixture which is white light into its components and reveal colors. 'Of Colours' contained all the elements of the theory woven together into one argument as they were to be again in the Opticks. Why should he have neglected an essential aspect of the argument

(1838). LXXIII. Observations on sulphurous aether, and sulphate of aetherine (the true sulphuric aether). The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science: Vol. 12, No. 77, pp. 474-480.

The researches by which Sir Joseph Larmor will chiefly be remembered belong to the decade 1892-1901, which is now recognized as a transition period in physics. After half a century of rapid progress, the main wave of advance seemed to have spent its force; and it was beginning to be said that the possibilities of discovery were approaching exhaustion. Before the end of the decade X-rays, electrons and radio-activity had again set experimental physics in feverish progress, to be followed later by revolutionary changes in the foundations of physical theory. But at the time when Larmor started on his main work there was little to inspire new ideas. The ever-urgent problem of the ultimate relation of matter and electricity and aether, and the search for a unifying conception which would explain how they come to possess their fundamental properties, had occupied the greatest minds of the time; and it was hard to see any direction in which new light might be found. The ground had been gone over again and again, and impassable barriers seemed to have been reached. Classical physics was indeed near the end of its tether. Of those who yet contrived to make substantial progress at this difficult stage—who brought classical physics finally to the point where new methods became inevitable—two names stand out prominently, Lorentz and Larmor. Their work had much in common, so that it is sometimes difficult to assess their contributions separately. Larmor’s reputation has perhaps been overshadowed by that of Lorentz. But on any estimate, Larmor’s achievements rank high; and his place in science is secure as one who re-kindled the dying embers of the old physics to prepare the advent of the new.

The Michelson-Morley experiment, performed in Cleveland in 1887, proved to be the definitive test for discarding the Fresnel aether hypothesis which had dominated physics throughout the 19th century. The experiment had been suggested to Michelson by his study of a letter of James Clerk Maxwell, and a preliminary but inconclusive trial had been made at Potsdam in 1881. It seems certain that the experiment would never have been repeated except for the urging of Kelvin and Rayleigh at the time of Kelvin's Baltimore Lectures in 1884, which Michelson and Morley attended. The conclusive null result of the Cleveland experiment was decisive in its influence on Lorentz, FitzGerald, Larmor, Poincare, and Einstein in developing their theories of the electrodynamics of moving bodies, which culminated in the special theory of relativity. The present account contains material from extensive notes and correspondence related to the work of Michelson and Morley which the writer has assembled during the past years.

It is possible that the negative result of the Michelson-Morley experiment is compatible with the existence of a medium or ‘aether’ if the latter is carried along with the Earth. The consequences of this model for phenomena due to the Earth ’s rotation (such as the precessional couple on a gyro-compass) are considered. An experiment has been carried out to compare the precessional couple at the Earth ’s surface with that at a depth of 3300 m to an accuracy of 1 part in 10 4 . The result was a negative one in that no change with depth was detected to this accuracy. The experiment is not quite accurate enough to rule out the ‘tied ’ aether hypothesis entirely but the depth for complete tying would have to be large compared to the Earth ’s radius to agree with the measurements. To this extent the hypothesis must be regarded as an unlikely one.

(1920). LXIV. A fluid analogue for the aether. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science: Vol. 39, No. 234, pp. 651-659.

1. In a recent papers the present writer discussed Dirac's new formulation of the quantum mechanics of the electron from the point of view of the wave theory. In the course of that work formulæ were obtained for the electric density and current associated with any type of electron wave. These formulæ link the electron with the æther, so that to a first approximation (that is, excluding such questions as the reaction of its own emitted radiation on the electron) we have a complete expression of the state of affairs, which is suitable for use in the classical electromagnetic theory. But there are certain problems in which it is convenient to attribute part of the magnetic field of a moving electron to an electric convection current and part to its intrinsic magnetisation; for example, this would be so in discussing the Stern-Ger1ach effect for free electrons. In the earlier paper a separation of this kind was carried out for an electron in an atom and a short account was given of the corresponding case for an electron moving freely. As the paper was intended to cover a much wider field, these matters were only reviewed rather briefly, and the purpose of the present note is to elaborate them somewhat more fully. The process is one of pure classical theory, for the establishment of current and density is the only appeal that need be made to the quantum theory. We shall exhibit directly the magnetic moment of the electron, working it out in the first instance for slow motions, as it is easy to generalise this case by relativity principles. It would no doubt be possible to develop the whole result in one step, but the purely classical problem of the fields of a swiftly moving magnet is quite troublesome, even though the principles have been fully mastered, so that it would be an unnecessary and profitless exercise to follow this procedure. It may be recalled that Dirac's equations were easily shown to be invariant for any space or relativity transformation, even though their form is quite unsymmetrical. The associated density-current functions naturally have the property of covariance, though also quite unsymmetrical in appearance. We shall here meet other tensors, also quadratic in the Ψ’s, and having the same unsymmetrical appearance. Their construction is by no means obvious, and the only process seems to be a direct application of all the transformations of the group to each component—a straightforward but laborious method. Before Dirac’s equations were found one would have said without hesitation that the correct procedure in such a case would be to reduce the equations themselves to tensor form, for then the associated tensors should become obvious. It is not hard to throw the equations into space-vector form, but if the relativity transformation is to included, they obstinately refuse to go into any but a very clumsy form and nothing is gained; this being so, it seems not worth while to use the space-venctor either. I have the hope that this subject may interest some analytical geometer and may tempt him to investigate these curiously unsymmetrical invariant properties. As we shall see, they appear to be connected with the stereographic projection of a sphere and perhaps with the homographic transformations of a complex variable, subjects with which I am not very familiar.

1. In two previous memoirs* it has been explained, that the various hypotheses involved in the theory of electric and optical phenomena, which has been developed by F araday and Maxwell, can be systematized by assuming the aether to be a continuous, homogeneous, and incompressible medium, endowed with inertia and with elasticity purely rotational. In this medium unitary electric charges, or electrons, exist as point-singularities, or centres of intrinsic strain, which can move about under their mutual actions ; while atoms of matter are in whole or in part aggregations of electrons in stable orbital motion. In particular, this scheme provides a consistent foundation for the electrodynamic laws, and agrees with the actual relations between radiation and moving matter.

1. In a previous paper the concrete representation of electrical and optical phenomena by means of a rotationally elastic fluid aether has been discussed. In an Appendix it has been shown that whenever there is direct question of interaction between the molecules of matter and the aether, whether it be in the phenomena of magnetism or in the optical phenomena of dispersion and moving material media, the consideration of groups of electrons or permanent strain-centres in the aether, which form a part of, or possibly the whole of, the constitution of the atoms of matter, suffices to lead to a correlation of the various modes of activity; while this scheme seems to be free from the chief difficulties which have pressed on other methods of representation. The present paper is chiefly concerned with the further development of the molecular aspect of this theory. As a preliminary, it is maintained that a dynamical theory of electric currents, based on the ordinary conception of a current-element, must lead to expressions for the electrodynamic forces which are at variance with the facts. On the other hand, a theory which considers moving electrons to be the essential elements of the true currents in material media, gives a definite account of the genesis and the mutual relations of both types of forcive, the electromotive and the ponderomotive, and gives formulae for them, which correspond in the main with those originally deduced by Maxwell from consideration of the properties of his concrete model of the electric field, though they are not substantiated by his later abstract theory based on current-elements. That theory is held to be defective, in the first place on account of the discrepancy with experiment above mentioned, and in the second place, because it is not competent to describe the mode of genesis of a conduction current by electrical separation produced in the element of volume of the conductor under the influence of the field of force; it is thus an incomplete formulation of the phenomena.

Nothwithstanding the well-known "principle of relativity," it is theoretically possible to determine the motion of the solar system with respect to the aether from observations of the eclipses of Jupiter's satellites; and the possibility was indicated by Maxwell some 30 years ago. For convenience, the motion of the aether with respect to the sun may be called a wind, and the method proposed is based on the consideration that the tidings of an eclipse will travel towards us more rapidly when the Jovian system is to windward of us than when it is to leeward. The residual discrepancies between the observed and calculated times of eclipses have to be analysed for systematic differences depending on the direction in space of the straight line drawn from the earth to Jupiter, and formulae are given for finding by the method of least squares the most probable values of a, b1, c1, the components of the Sun's velocity with respect to the aether. The material available is to be found in Prof. R. A. Sampson's discussion of the Harvard photometric eclipse-observations; about 330 eclipses of Jupiter's satellite I being included. In order to obtain a preliminary notion of the accuracy to be expected, a simplified system has been considered in which (for one thing) the eccentricity of the orbits was virtually neglected; and it appears that some advantage is to be gained by taking the plane of Jupiter's orbit, rather than the ecliptic, as one of the coordinate planes. The axis of x is drawn from the Sun's centre through the node of Jupiter's orbit, the axis of y lying also in that orbit, and the axis of z being perpendicular thereto. Taking 4.5 seconds as the "probable" discrepancy between theory and observation for a single eclipse, the following preliminary estimates are obtained:- Probable error in a = 43.6 km. per second. Probable error in b1 = 45.6 km. per second. Probable error in c1 = 10,000 km. per second. The determination of the component perpendicular to Jupiter's orbit is perhaps too badly conditioned to be worth considering; the two components in the plane of Jupiter's orbit can be much better computed, and even if the velocities found do not exceed the probable limits of error, an upper limit to the numerical values of those components can be assigned.

1. In two previous memoirs* it has been explained, that the various hypotheses involved in the theory of electric and optical phenomena, which has been developed by F araday and Maxwell, can be systematized by assuming the aether to be a continuous, homogeneous, and incompressible medium, endowed with inertia and with elasticity purely rotational. In this medium unitary electric charges, or electrons, exist as point-singularities, or centres of intrinsic strain, which can move about under their mutual actions ; while atoms of matter are in whole or in part aggregations of electrons in stable orbital motion. In particular, this scheme provides a consistent foundation for the electrodynamic laws, and agrees with the actual relations between radiation and moving matter.

An experiment is described showing that a cylindrical condenser rotating inside a magnetized coaxial solenoid becomes charged as required by the theory of Lorentz. Rotation of the solenoid has no e...

A short section of Aristotle's de generatione animalium embodies his final answer to the question how the faculties of soul are transmitted from parent to offspring. Aristotle here speaks in a tone which is dogmatic as well as enthusiastic; he is able to announce a new discovery. There is, he sets forth, in the sperma a peculiar substance (σῶμα) which has some connection with soul and differs in quality as the souls themselves differ in worth. This substance is identical with two of the entities mentioned in our title and ‘analogous’ to the third.Πάσης μὲν οὖν ψυχῆς δύναμις ἑτέρου σώματος ἔοικε κεκοινωνηκέναι καὶ θειοτέρου τῶν καλουμένων στοιχείων ὡς δὲ διαφέρουσι τιμιότητι αἱ ψυχαὶ καὶ ἀλλήλων, οὕτω καὶ ἡ τοιαύτη διαφέρει φύσις. πάντων μὲν γὰρ ἐν τῷ σπέρματι ὑπάρχει ὅπερ ποιεῖ γόνιμα εἶναι τὰ σπέρματα, τό καλούμενον θερμόν. τοῦτο δ᾿ οὐ πῦρ πὐδὲ τοιαύτη δύναμίς ἐστιν, ἀλλὰ τὸ ἐμπεριλαμβανόμενον ἐν τῷ σπέρματι καὶ ἐν τῷ ἀφρώδει πνεῦμα καὶ ἡ ἐν τῷ πνεύματι φύσις, ἀνάλογον οὖσα τῶν ἄστρων στοιείῳ.The sentences which follow state that fire has no generative or procreative power, yet such a power must be present in the Sun and in the θερμόν, the vital heat of living beings. Clearly, then, this θερμόν cannot be identical with the fire.Nowhere else in the body of his preserved work does Aristotle establish this close connection between the vital heat, the pneuma, and the element of the stars, the so-called aether. These three concepts differ as much in their origin and past history as in their function and place within Aristotle's own physical or biological system. A brief sketch of them—skipping by necessity many significant episodes in the history of each—will suffice to make this clear.What needs here to be said about the ‘element of the stars’ is indeed not much. It was Aristotle himself who added this element to the canonic four of the Empedoclean and Platonic tradition. The dialogue On Philosophy and the First Book On the Heaven secured it its place. It is divine, un-ageing, and unchanging, and yet a material element. Like the other elements it has its specific ‘natural motion’, to wit the circular, which makes it possible for Aristotle to explain by a physical ‘hypothesis’ the celestial motions for which Plato had resorted to the World-Soul. The place of this element is the entire heavenly region, extending from the First Heaven to the moon; below this, in the regions occupied by the four other elements, it is never to be found.

(1823). XV.—On the combined action of heat and pressure on water, sulphuric aether, and rectified oil of petroleum. The Philosophical Magazine: Vol. 61, No. 297, pp. 58-61.

(1904). XXXVII. On double refraction in matter moving through the AEther. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science: Vol. 7, No. 40, pp. 317-329.

The experiments described in this paper were designed with the object of investigating the behaviour of a charged electrical condenser moving through space, and to discover, if possible, whether there be a relative motion between the earth and the æther. It was previously suggested by one of us in the ‘Proceedings of the Royal Dublin Soc.’ (Vol. VII., Part XIV., April, 1902), in connection with an experiment of a similar nature suggested by the late Professor FitzGerald, and mentioned in his collected papers edited by Professor Larmor. The idea underlying the experiments will be understood from the following considerations :—If a charged condenser be placed with its plane in the direction of the æther drift, then, on the assumption that a moving charge develops a magnetic field, there will be associated with the condenser a magnetic field perpendicular to the lines of electric induction and to the direction of the motion. When the plane of the condenser is perpendicular to the æther drift, the effects of the opposite charges will neutralise each other. Thus there is magnetic energy stored in the medium when the plane of the condenser and the direction of the drift coincide; and accordingly it is to be expected that under these circumstances the condenser, when freely suspended, would tend to move so as to take up the position with its plane perpendicular to the drift, in order to transform this energy.

Summary The fact that light manifestations according to Maxwell require an aetheric and not a material medium calls for an interpretation of Gladstone and Dale's so-called molecular refractive idnex m. Such index really refers to the non-material medium of molecular diameter dm surrounding and attached to the nucleus. It is shown that by coordinating the Gladstone and Dale rule with that of Lorentz and Lorenz that the molecular index m becomes a function of the material density of the medium, and incidentally, therefore, a function of the temperature. Any increased value of m with density is to be ascribed to a further proportional filling up of the intermolecular space with a modified aetheric medium, so that eventually no pure (numodified) aether exists between the nuclei. Whereas, however, the intrinsically attached non-material medium moves with the individual nuclei (Bradley aberration effect), relative motion is assumed possible (Fizeau effect) between the molecules of diameter dm and the modified aethe...

While aether drift experiments originally suggested the line of thought which led to the formulation of the restricted theory of relativity, it would seem that the fundamental significance of that theory does not depend primarily upon these experiments. The most logical origin of the transformation of the restricted theory is to be found as a special case of the general theory, and the purpose of the present paper is to show how, with this in view, the fundamental working content of the restricted theory, the invariance of laws under the Lorentzian transformation, is something which has no fundamental relation to the question of whether the aether drift experiments do or do not give a positive result.

There is an outstanding gap in electromagnetic theory in respect to the attempt to reconcile the analysis of æthereal stress on the lines initiated by Maxwell with Newton’s third law and the law of the conservation of energy. In the present condition of theory there is assigned to the æther a certain distribution of electromagnetic energy and momentum. The hypothetical distribution of energy is necessarily associated with the Poynting vector which measures its rate of transference. The distribution of momentum is so defined that the rate of increase of the total amount, within any given volume supposed at rest in the æther, is equivalent to the resultant of the Maxwell stresses on the bounding surface. There is, however, no connection established between the transference of energy across an area and the stress across that area. Such a connection would require that it should be possible to assign to the medium in which stress and energy reside a state of motion whereby the stresses might do the necessary amount of work, and this again would require the revision of the specification of stress, inasmuch as the ordinary expressions are computed for an element of surface which is at rest. Numerous other questions arise as soon as such a process is attempted, but the present paper seeks only to analyse what types of motion must be looked for, and to specify the field of stress upon the elements of area moving with the velocities obtained. Strictly, it is incorrect to speak of the stresses on elements of area in the æther at the same point having different velocities. The true stress in a continuous medium can only be estimated on an area moving with the medium. All that can be done in the absence of a knowledge of the velocity of the medium is to analyse the transference of momentum across an element of area having a specified velocity. Only when this velocity is that of the medium is it legitimate to interpret this transference as due to a state of stress in the medium. Thus, unless the æther is supposed at rest, the Maxwell expressions have no significance, except as giving the rate at which momentum is crossing an element of area at rest. If, however, the æther is assumed at rest, then no state of stress can give rise to any transfer of energy. 1. The flux of momentum across an element of area moving with velocity v differs from that across a similar element at rest by the vector v v g per unit area, g being the intensity of the electromagnetic momentum (=[EH]/4 πc ) and v v being the component of v normal to the area.

(1866). XXXII. A speculation concerning the relation between the axial rotation of the earth, and the resistance, elasticity, and weight of solar AEther. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science: Vol. 31, No. 208, pp. 210-213.

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(1910). XI. Spontaneous generation of electrons in an elastic solid aether. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science: Vol. 19, No. 109, pp. 129-152.

(1904). LXXII. Relative motion of earth and aether. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science: Vol. 8, No. 48, pp. 716-719.

In his recent paper, ‘Newton’s Optical Aether’ (i), Professor Guerlac has uncovered much of interest in explanation of the format of the second English edition of the Opticks . That Newton intended that there should be a ‘Part II’ to the third book of the Opticks , seems now to be irrevocably proved, as also is the fact that the contents of this part were to include some of the electrostatic experiments of Hauksbee. It has previously been Professor Guerlac’s contention that these experiments of Hauksbee’s formed a distinct part in a revival of Newton’s belief in an aetherial medium (2), and in this recent paper he further suggests that for more, ‘persuasive experimental confirmation’ of the aether hypothesis, Newton devised the ‘two-thermometer experiment’ (3). I should like to suggest, and later in this paper to expound, that Newton’s interest in Hauksbee’s experiments, which were mostly performed between the years 1705-1712 (4), was related to a general interest in electrical phenomena and a specific interest in the attractive and repulsive forces exerted between the smallest particles of matter. Initially, however, there are other points which deserve of further consideration.

STUDENTS of Newton’s physical thought are now in rather general agreement that—contrary to what various writers have asserted—a belief in an aetherial medium was not throughout his life ‘a central pillar’ of Newton’s system of nature (i). By the time he wrote the Principia , it seems clear, Newton had not only rejected the Cartesian dense aether, but had come to distrust his own youthful aetherial speculations (2); from the 1680’s until some time after 1706, the year the Latin translation of his Opticks appeared, an aether played little or no role in Newton’s conjectural system of nature.