SCIENCE- GOSSIP. 



349 



CONDUCTED BY JAMES QUICK. 



Seat of the E.M.F. in" a Voltaic Cell. — 

 This formed the subject of the presidential address 

 recently given by Professor Oliver J. Lodge to the 

 Physical Society. He said : — " Strange that a dis- 

 covery of this magnitude, and I may say also, in one 

 sense, of this simplicity, should have been associated 

 with a controversy which, arising in one form almost 

 directly it was announced, has continued, with slight 

 modifications and with temporary lulls, yet really 

 without cessation, throughout the whole century; I 

 hardly know of another instance of a question to 

 which every physicist in the world must necessarily 

 at some time or another have given his attention 

 remaining so long unsettled. What is the seat of the 

 chief electromotive force in the voltaic pile ? " Pro- 

 fessor Lodge then discussed the controversy from the 

 contact and the chemical sides. The opposing sides 

 of the old controversy used to be called "contact 

 theorists" and "chemical theorists. "' Now the opposite 

 sides are involved both in contact and both in chemical 

 views. It is a question of which of several contacts 

 is the effective one, and what kind of chemical action 

 or affinity is the active cause. Is it the contact and 

 chemical affinity across the metal-metal junctions 

 or across the metal-air junctions ? The opposite 

 sides are thus metallic and dielectric. The metal-air 

 force is of the order volts ; the metal-metal force is of 

 the order millivolts. When a piece of zinc is put in 

 contact with a piece of copper, the oxygen atoms 

 which surround these bodies move slightly away from 

 the copper and approach slightly nearer to the /inc. 

 These slight motions produce the whole Volta effect. 

 -Vll that is necessary for the Volta effect is the inherent 

 film on the surface ; all the rest of the gas is mere 

 dielectric, and might be substituted by a vacuum. 

 The safest and clearest mode of expressing the Volta 

 effect is that it consists in an opposite charge acquired 

 by dry zinc and copper while in metallic contact — a 

 charge which results from an E.M.F. of fixed value 

 and is controlled solely by this E.M.F. and electro- 

 static capacity. 



Fluorescent Screens. — When Rontgen-ray 

 observations are made by means of fluorescent screens, 

 a certain short time is found to elapse before the X-ray 

 picture is built up. The bones of the hand, for instance, 

 are not visible at once on the screen ; they gradually 

 separate out from the flesh. This effect is only 

 partially due to a change in the radiation impinging 

 upon the screen. What is known as a "hard'" 

 X-ray vacuum tube produces radiographs with 

 greater contrast than "soft" tubes do, and the 

 above effect might be put down to the hardening of 

 the tubes while in action. On the other hand, how- 

 ever, a gradual and distinct brightening of the screen 

 is observed, which is quite independent of any change 

 in the radiation and is unaccompanied By any ob- 

 servable change of colour or chemical constitution. 

 Some experiments made in this direction recently 

 by Precht show that the time required for a good ■ 

 development of the radioscopic picture is on the 



whole shortest at the highest discharge potentials. It 

 varies from a few seconds to a minute. A feasible 

 explanation of this phenomenon lies in an allotropic 

 modification of the substance of the screen, as sup- 

 ported by Pecquerel for radium rays. Precht, how- 

 ever, puts forward an emission hypothesis for Rbntgen 

 rays. 



Professor D. E. Hughes. — At a recent meeting 

 of the French Academy of Sciences it was announced 

 that the late Professor Hughes had bequeathed to 

 that institution a sum of ,£4,000, the income of 

 which is to be used as a prize for the most important 

 discovery in Physical Science, preference being given 

 to a discovery in electricity or magnetism. A similar 

 announcement was made by the President at a meet- 

 ing of the Institution of Electrical Engineers a few- 

 weeks ago, to the effect that Professor Hughes had 

 bequeathed the sum of ^2,000 for the foundation of 

 a " David Hughes Scholarship" in connection with 

 the Institution. 



Electric Fish of the Nile. — Under this 

 heading a note appeared in the " Physics" column of 

 Science-Gossip for May 1899, p. 372, when par- 

 ticulars were given of Professor Gotch's lecture 

 delivered at the Royal Institution on March 17th of 

 that year. Professor Gotch's hypothesis was that the 

 seat of the electromotive force in the fish known as 

 the Malaplerunts electricits lies in the nerve centre 

 itself, and not in the so-called electric organ. Some 

 recent experiments by Professor Gotch and .Mr. G.J. 

 Burch point still more conclusively to this hypothesis 

 being the correct one. One of Mr. Burch's capillary 

 electrometers was used for measuring the values of 

 the electromotive force. The fish experimented upon 

 was firs', anaesthetised and then killed, and a strip of 

 the electric organ with the nt:r\c was carefully dis- 

 sected out and kept at a temperature of 5 J C. The 

 time-lag between the excitation of the nerve and the 

 record of an E.M.F. was then observed. From the 

 various results obtained, the authors think it probable 

 that the greater part of the time was occupied by the 

 slow transmission of the excitatory slate along the 

 finest subdivision of the nerve within the organ near 

 the ultimate ends. In dissecting the anaesthetised 

 animal Professor Gotch received a strong shock 

 while dividing a nerve-branch with metal scissors, the 

 organ being grasped with' metal forceps. After a 

 comparatively few successful experiments the ex- 

 citability of the nerve suddenly failed, and this was 

 attended by inability of the organ to respond, whether 

 a stimulus was applied to the nerve or to the organ 

 substance. Measurements of the resistance of the 

 organ were made, and it was found by taking read- 

 ings longitudinally to the column and transversely, 

 i.e. across and parallel to the " discs " respectively, 

 that the resistance of the thin "disc*" was consider- 

 ably higher than that of the albuminous composition 

 between them. If Professor Gotch's theory is the 

 correct one, then what is the function of the so- 

 called electric organ ? May it not combine the duties 

 of condenser and connection board? It may be for 

 this reison that the "discs'" are formed thin and are 

 of high resistance to serve as dielectrics between 

 the conducting albuminous fluid in the compartment 

 spaces. 



Searchlights. — A new portable electric search- 

 light is reported to have been recently added 1*1 the 

 equipment of the New Vork fire brigade, for use at 

 night fires or where the smoke is very dense. The 

 lamp takes 35 amperes of current, and will emit a 

 light of about 6.000 candle-power. 



