March 26, 1885] 



A A TURE 



499 



polarisation of the medium between two oppositely charged 

 conductors, the direction of polarisation being at right angles 

 to these bands — i.e., in the line joining the conductors — the 

 medium in this I Leyden jar, the two 



opposite electrifications being represented by the tight and loose 

 bands, one conductor being bounded entirely by tight bands and 

 and the other by loose ones, and the electric displacement of 

 Maxwell being represented by the difference between the two 

 sides of a band. If the bands along any line between the 

 I. all the energy of the medium was spent 

 along this line in friction, and this represented a discharge along 

 the line. Thi= energy was conveyed into the line of discharge by 

 and not along its length in accordance with what Prof. 

 Poynting has recently shown to be the case in all electric currents. 

 If the resistance along the line of discharge were sufficiently small 

 the momentum of the wheels would carry them beyond their 

 in ol equilibrium and the well-known phenomenon of an 

 would be represented. This led to the 

 . ition that the magnetic displacement was represented by 

 the angular velocity of relation of the wheels and the self- 

 induction by their momentum. It was remarked that the 

 mechanical attraction between the two conductors was not 

 represented, but it was explained that as this depends on the 

 connection of matter with ether it would require more compli- 

 cated mechanism. It was, however, pointed out that by 

 supposing the wheels slightly distorted by the stress, and by 

 ising a thread wound around them and each end connected 

 with the material of a conductor, a force would be produced 

 drawing the conductors together owing to the circumfer- 

 ence of a ' eel being longer than of an lin- 

 ed one. This force would be proportional to the 

 square of the distortion, a necessary condition not satisfied by 

 ordinary Stresses, and would be, if exerted between two infinite 

 ties, independent "I their distance apart, and so must represent 

 varying inversely as the square of the distance. Ketum- 

 the electric currents, it was shown that by turning the 

 if a conducting circuit the whole region u as 

 filled with turning wheels — i.e. , with magnetic displacement — and 

 that, if a resistance were introduced at any point of the circuit, 

 the energy would be transferred to that point through the medium 

 and enter by the side of the conductor. If two independent 

 conducting circuits existed near one another it was shown that 

 the phenomena of induced currents were represented. It was 

 explained that the mechanical force was not represented, as it 

 led upon the connection between matter and ether, 

 but that it might be looked for as in some way depend- 

 1 in the centrifugal force arising from the rotations. 

 The equations representing the energy of the model are 

 of the same form as those of Maxwell representing the 

 ■ of the 1 hi 1 when limited by the consideration that the 

 1110 -Id was only in one plane. It was explained that a tridimen- 

 model whose energy could be represented by the same 

 ions as Maxwell's could not be a instructed with indiarubber 

 , but might be constructed by means of wheels pumping 

 tluid through pipes. This led to the observation that the 

 propagation of waves by transverse vibrations could be illustrated 

 by the model, and it was explained how a sudden turning of any 

 set of wheels would start a wave-pr pagation whose direction 

 of propagation was at right angl. s to the directions of magnetic 

 cement and of electric displacement, the former repre- 

 11 and the latter by the line joining 

 the centres of a tight and It would be pos- 

 theoretically to construct a model illustrating the laws 

 lection and refraction of light even at the surfaces of 

 iline media, and to reproduce conical refraction. It was 

 ined that by twisting the medium the rotatory polarisation 

 utz might be represented, and that probably a mechanism 

 might be introduced by which the rotation of other wheels or of 

 something besides the wheels being altered by the rotation of 



Is, a i 11 of the former on the latter would 



duce magnetic rotatory polarisation. It \\.i, pointed out that 

 magnetic rotatory polarisation and dispersion were due to a 

 reaction of the medium during the wave-propagation and nut to 

 1 change of the medium independent of the wave-propagation. 

 It was explained that it was not to be supposed that the clher 

 was constructed of wheels and indiarubber* bands, nor even of 

 wheels pumping fluid in pip pointed out that some 



1 tics of the ether might be gathered from the model if it be 

 assumed that the qualities of the ether represented by symbols 

 obeying the law s of rotation for instance are really of the nature 

 of rotation. If this be so the ether must be such that any part 



of it can rotate as often as it likes provided all the neigh- 

 bouring parts rotate equally and the electrostatic stresses in 

 the ether must be due to the difference of rotation of its parts. 

 If the ether be a perfect liquid it can only have such pro- 

 perties as represent rigidity by being in motion, and it u as 

 explained that many electrical phenomena might be illustrated 

 by the polarisation of the vortical motions in a vortex-sponge. 

 Sir \Ym. Thomson has pointed out that such a state of polaris- 

 ation as a single vertex region in the centre of a cylindrical box 

 wdll not of itself change unless it can spend its energy on the 

 box, which is quite analogous to the fact that the energy of the 

 polarisation of the ether does not disappear unless it can produce 

 heat or mechanical or other forms of energy. It was also 

 pointed out that forces depending on small vortices vanished at 

 small distances from them and that hence the forces depending 

 on their polarisation between two infinite planes would depend 

 on the polarisation and not on the distance between the 

 planes, and so must be of the nature of forces varying 

 inversely as the square of the distance. It was explained 

 that the modes of polarisation of vortices were sufficient to 

 explain both electrical, magnetic, cohesional and chemical forces. 

 It was finally reiterated that the only possible way of giving 

 anything of the nature of rigidity to a perfect liquid was by 

 conferring motion on it and that it seemed likely that any 

 mechanical properties could be conveyed by suitably chosen 

 motions. This was quite in accordance with Sir Wm. 

 Thomson's suggestive address to Section A at Montreal. 



Natural Science Section.— V. Ball, M.A., F.K.S., in the 

 chair. — On the physical characters of calcareous and siliceous 

 sponge spicules and other structures, by Prof. W. J. Sollas, M. A., 

 D. Sc. , F. R.S. E., F.G. S. — The refractive index of a siliceous 

 sponge spicule, diatom, or other siliceous organic body is 

 determined by immersing it in liquids of different refractive 

 indexes until one is found in which it ceases to be visible under 

 the microscope. The refractive index of this liquid gives that 

 sought for. 1 he siliceous matter of organisms has a refractive 

 index of I '449, which is that of some kinds of opal or colloidal 

 silica. The refractive indexes of calcareous sponge spicules are 

 found in a similar manner, but as these are biaxial it is necessary 

 to examine them between crossed Nicols ; r, = i"485, r„ = l'6S9. 

 These indexes agree with those of calcite. This method of 

 obtaining refractive indexes is applicable to mineral bodies ; the 

 glass of the Krakatoa explosion is thus found to have a refractive 

 index of I '51. Leucite can be thus readily distinguished from 

 analcime and calcite from aragonite. The specific gravity of 

 calcareous spicules ( I '62) and that of foraminifera were found by 

 an adaption of the Sonstedt solution method to use with the 

 microscope. The perforate foraminifera have a sp. gr. of 2 '65 

 to 2 '67, the imperforate of 27 to 272, calcite being taken as 

 2'7. The structure of calcareous spicules was shown by a study 

 of the extinction angles between crossed Nicols, by the develop- 

 ment of cleavaie planes, and each figures to be purely crystalline. 

 Each spicule is a single calcite individual with its optic axis 

 definitely related to its form. The acerate spicules of calci- 

 sponges are distinguished from those of the siliceous sponges by 

 their form, the former often presenting an oval or rhomboidal 

 transverse section. The large spicules of the Pharetrones agree 

 with those of the Calcisponges, with which, therefore, this fossil 

 group must be associated. — On some Trilobites from the Cambro- 

 Silurian rocks of the County Clare by W. H. Baily, F.C.S.— 

 Notes on the coalfields of Leinster and Tipperary by G. H. 

 Kinahan, M.R.I. A. 



Cambridge 



Philosophical Society, March 2. — Prof. Foster, President, 

 in the chair. — The following communications were made : — On 

 some theorems in tides and long-waves, by the Rev. E. Hill. 

 Elementary considerations were given from which it might be 

 inferred that when a disturbing body produces a semi-diurnal 

 tide in an equatorial canal, the point nearest to the disturbing 

 body will be a point of low tide or high tide according to the 

 depth of the canal. A general explanation was given of the 

 influence of the depth of a canal on the speed of a long wave 

 traversing it. It was shown that the ordinary formula for this 

 speed might be deduced from the ordinary differential equation 

 of motion without integration. — On the electrical resistance of 

 platinum at high temperatures, by Mr. W. N. Shaw. — On an 

 automatic mechanical arrangement for maintaining a constant 

 high potential, by Mr. Threlfall. A water-motor of the Thirl- 

 mere type is allowed to settle down to a constant velocity by 

 means of the resistance of a fan which is worked by the motor. 



