482 



NATURE 



\_March 29, 1877 



SOCIETIES AND ACADEMIES 

 London 



Royal Society, January i8. — "Residual Charge ot the 

 Leyden Jar. — 11. Dielectric Properties of Various Glasses," by 

 J. Hopkinson. Communicated by Prof. Sir William Thomson, 

 F.R.S. 



The experiments appear to verify the fundamental hypothesis, 

 viz. , that the effects on a dielectric of past and present electro- 

 motive forces are superposable. Ohm's law asserts the principle 

 of superposition in bodies in which conduction is not complicated 

 by residual charge. Conduction and residual charge may be 

 treated as parts of the same phenomenon, an after effect as 

 regards electric displacement, of electromotive force. The ex- 

 periments appear to show that tlie principle of Ohm's law is 

 true of the wliole phenomenon of conduction through glass. 



February i. — " The Meteorology of the Bombay Presidency," 

 by Charles Chambers, F.R.S., Superintendent of the Colaba 

 Observatory. 



This work consists of four parts — the first dealing with regis- 

 trations of meteorological phenomena at the Colaba Observatory 

 during a period of twenty-seven years ; the second with mode- 

 rately fall observations at five military stations in the Bombay 

 Presidency during a period of nineteen years ; and the third with 

 large numbers of observations from civil hospitals and revenue 

 stations, being those of selected registers extending over various 

 periods from not less than a fortnight up to a number of years ; 

 in this part the phenomena treated are temperature of the air, 

 winds, and rninfall only ; and the extent of territory to which 

 the observations refer includes the whole of the Presidency, Sind, 

 and the western half of Rajputana. In the fourth part are dis- 

 cussed the general distribution (as regards both space and 

 season) of temperature and rainfall, and the variations of the 

 wind ; first with respect simply to the physical geography of the 

 country, and then in combination with certain theoretical views, 

 the elucidation of which, by means of the dynamical theory of 

 heat and the kinetic theory of gases, occupies much space. 



February 15. — "On Stratified Discharges. — III. On a Rapid 

 Contact-Breaker, and the Phenomena of the Flow." By 

 William Spottiswoode, M.A,, F.R.S. 



In a paper published in the Proceedings of the Royal Society, 

 vol. xxiii. p. 455, I have described a form of contact-breaker 

 designed for great rapidity and steadiness of action. It con- 

 sisted of a steel rod which vibrated under the action of an electro- 

 magnet. As regards sharpness of break and steadiness of the 

 striae, this instrument left little to be desired. But, as explained 

 in the paper, an alteration in the current not only affected the 

 steadiness directly, but also reacted on the break itself. In 

 order to obviate this inconvenience, I devised another form of 

 contact-breaker consisting of a wheel platinised at the edge, 

 on which a platinum spring rests. In the circumference of the 

 wheel a number (40 in the first instance) of slots were cut, and 

 filled with ebonite plugs so as to interrupt the current. The 

 breadth of the slots was about '04 inch, and that of the teeth about 

 •5 inch. The wheel was connected with suitable driving gear, 

 so as to give from 250 to 2,000 currents from the coil in each 

 direction per second. 



For some time the experiments were conducted with the plati- 

 num spring resting on the wheel ; and the effects were varied by 

 altering either the pressure of the spring or the velocity of the 

 wheel ; but it: was (ovmd that actual metallic contact between the 

 spring and wheel was not necessary, provided that a layer or 

 cushion of conducting material were interposed. Such a layer 

 was formed by a thin film of dilute sulphuric acid drawn out 

 by a thread leading from a reservoir and resting on the wheel. 

 The spring, which under these circumstances became unneces- 

 sary, was replaced by a point, the adjustment of whose distance 

 from the wheel was simple. This arrangement gave excellent 

 results, even when the number of currents per second was re- 

 duced in some cases to 250 ; added to which the unpleasant and 

 disturbing noise of the friction was entirely avoided. Ulti- 

 mately, however, I used a light wire in the place of the spring 

 first mentioned. 



With the contact-breaker here described effects similar to 

 those produced by the rapidly-vibrating break were obtained. 

 The strias were formed in a regular manner, and advanced or 

 receded, or remained at rest, in a column usually unbroken so 

 long as the velocity of the wheel was maintained without 

 change. 



With a view of ascertaining the nature of the distinction be- 

 tween the ordinary and the steady striae, careful observations were 



j made with the revolving mirror. It having been noticed that 

 when the wheel-break moved slowly, ordinary or irregular striaa 

 j were produced, and that when it moved rapidly, steady striae 

 I resulted, it seemed probable that the latter effect might be due 

 I to the short time of contact, and to the consequent absence of 

 many of the features described in Part II. of these researches. 

 This is, in fact, identical with the suggestion there made, that 

 the fluttering appearance was due to the unequal duration of the 

 striae themselves, and to the irregular positions of the points at 

 which they are renewed at successive discharges of the coil. And 

 such, in fact, proved to be the case ; for as the speed of the 

 wheel was increased, the duration of the discharges diminished ; 

 the image as seen in the mirror became narrower and simpler in its 

 configuration, until, when the steady effect was produced, each 

 discharge showed only a single column of strice of a width pro- 

 portional to the apparent width of the slit. The proper motion, 

 implied by the inclination of the individual striae to the vertical, 

 was suU perceptible, and was directed as usual towards the 

 negative pole. 



The phenomena of the flow may be considered to be due to 

 the different positions taken up by the stride in successive dis- 

 charges. If in each discharge the strije occupy positions in 

 advance of those occupied in a previous discharge, the column 

 will appear to advance ; if the reverse ba the case, they will 

 appear to recede. If the positions remain unchanged, the 

 column will appear stationary. 



Experiments were instituted with a view of ascertaining the 

 connection between the flow and resistance. Starting from a 

 condition of current and break for which the striae were station- 

 ary, it was found that an increase of resistance, introduced gene- 

 rally in the primary circuit, produced a forward flow, i.e. from 

 the positive towards the negative terminal, while under similar 

 circumstances a decrease of resistance produced a backv/ard flo v. 

 Furthermore, if after producing a forward flow the resistance be 

 continually increased, the flow, after increasing in rapidity so as 

 to become undistinguishable by the unassisted eye, gradually 

 appears to become slower, and ultimately to reverse itself. 



Another form of contact-breaker was also occasionally used. 

 The principle upon which it was based was the sudden disrup- 

 tion of a thin film of conducting liquid by a discharge between 

 the electrodes of a circuit. 



As soon as the current passes, the fluid between the plate and 

 point will be decomposed, and electrical continuity broken. 

 This done, the fluid flows back again, and continuity is restore!. 



February 22. — " On a New Form of Tangential Equation," 

 by John Casey, LL.D., F.R.S., Professor of Higher Math.- 

 matics in the Catholic University of Ireland. 



'•' Addition on the Bicircular Quartic," by A. Cayley, LL.D., 

 F. R. S., Sadlerian Professor of Mattiera itics in the University of 

 Cambridge. 



Geological Society, March 7. — Prof. P. Martin Duncan, 

 F.R..S., president, in the chair. — The Rev. Ebenezer Davie.s, 

 William Da vies, and Henry Davis Iloskold were elected Fel- 

 lows, and George Garves Brush, Professor of Mineralogy in the 

 Sheffield School of Science, Yale College, Newhaven, Connec- 

 ticut, Prof. A. L. O. Descloizeaux, of Paris, Prof. E. Renevier, 

 of I^ausanne, and Count Gaston de Saporta, of Aix en Provence, 

 Foreign Correspondents of the Society.— The folio vving com- 

 munications were read : — On the vertebral column and pelvic 

 bones of Fliosaurus evansi (Seeley), from the Oxford Clay of 

 St. Neot's, in the Woodwardian Museum of the University of 

 Cambridge, by Harry Govier Seeley, F.L.S., Professor of Geo- 

 graphy in King's College, London. In this paper the author 

 described some bones obtained by J. J. Evans in the lower part 

 of the Oxford Clay at Eynsbury, near St. Neot's. They con- 

 sisted of thirty-seven vertebra?, twenty-one of which are cer- 

 vical, and apparently complete that series. These presented the 

 characters of the cervical vertebrae of the typical Pliosaurs of the 

 Kimmeridge Clay. The remains of the pelvis included a pubic 

 bone showing a close correspondence in form with those of the 

 Pliosaurs of the Kimmeridge Clay of Ely, and an ischium.— 

 Supplementary notes on the fauna of the Cambridge Greensand, 

 by A. J. Jukes-Browne, F.G.S. This paper was supplementary 

 to one communicated to the "Society by the author in 1875, in 

 which he maintained that the Upper Greensand does not ex- 

 tend further in a northwesterly direction than West End Hill, \ 

 near Cheddington, in Buckinghamshire, that the Cambridge 

 Greensand is merely a nodule- bed at the base of the Chalk Marl, 

 resting unconformably upon denuded Gault, to the upper part of 

 which _ the greater portion of the fauna belongs, and that the 



