5^4 



NA TURE 



[October 4, 1900 



proposes to obviate by substituting in the definition, for the 

 current at a given point at the given instant, the current which 

 existed at that point r/V seconds before, where r is the distance 

 of the point from that at which the vector potential is to be 

 measured, and V is the velocity of propagation of an electric 

 disturbance. 



The communication which most attracted the attention of the 

 members of the Association, and produced a great addition to 

 the attendance at Section A, was that of Sir William H. Preece 

 on wireless telephony. By a series of experiments carried out 

 at Lock Ness, the Menai Straits, the Skerries and at Rathlin 

 Island, he has shown conclusively that wireless telephony is a 

 practical and commercial system. At the Skerries a line half a 

 mile long terminated by earth plates placed in the sea, at a mean 

 distance of nearly three miles from a similar wire three and a 

 half miles long on the mainland, was quite sufficient to enable 

 telephonic messages to be transmitted with the ordinary instru- 

 ments. At Rathlin Island the wire is eight miles from the 

 mainland and communication is readily maintained. Endeavours 

 are to be made to extend the system to ships and there seems 

 •every probability of success. 



Prof. G. F. FitzGerald, in a note on Cremieu's experiment, 

 ■described the arrangement adopted by Mr. Cremieu and the 

 negative result he had obtained, and contrasted them with the 

 arrangement and result obtained by Rowland in his experi- 

 ments on electric convection made in 1876. He considered that 

 the discrepancy of the results of experiments, which appeared to 

 have been carried out with great care, did not necessarily dis- 

 prove our theory of electromagnetism, but rather signified that 

 there was some action of a moving ion not hitherto included in 

 our equations which was well worth investigating. Dr. J. 

 Larmor pointed out that any want of symmetry of the revolving 

 disc and fixed case in Cremieu's apparatus would tend to cause 

 some part of the charge on the disc to remain stationary. 

 Prof. A. Gray announced that he had already commenced 

 work with a view to repeating both Rowland's and Cremieu's 

 experiments with the same apparatus. 



Prof. J. Chunder Bose gave an account of his work on the 

 effect of electrical stimulus on inorganic and living substances. 

 By measurements of conductivity he determines the magnitudes 

 of the changes produced in the molecular structure of substances 

 due to an electric stimulus. Taking time of exposure to 

 stimulus, or time of recovery from effect of stimulus, as abscissae, 

 and change of conductivity as ordinates, he draws curves for 

 •numerous substances under varying conditions. He finds that 

 the curves for organic and inorganic substances are similar. On 

 this as a basis he has constructed an artificial retina, which has 

 enabled him to explain many obscure phenomena of vision. 



The Committee on Electrolysis and Electro-chemistry re- 

 ported that the experiments on the freezing points of the 

 solutions whose electrical conductivities had been found by Mr. 

 Whetham were still in progress. Some experiments on the con- 

 sumption of carbon anodes in electrolysis have been made by 

 Mr. Skinner, who has found that the anion produced by electro- 

 lysis of any highly oxidised material consists partly of carbonic 

 acid. The committee now lapses. 



Prof. G. F. FitzCxerald opened a joint discussion with the 

 chemical section, on ions. While acknowledging that the dis- 

 sociation theory of electrolysis had proved a useful hypo- 

 thesis, he wished to draw attention to the fact that there were 

 phenomena which it was incapable of explaining, and that dis- 

 sociation itself had not been dynamically explained. Why 

 should water dissociate a dissolved salt into its ions ? where 

 does the necessary energy come from ? how can the dissociated 

 ions wander about in the solvent without recombining ? and why 

 do some ions travel faster than others ? seemed to him questions 

 which the supporters of the theory had never satisfactorily 

 answered. The recent work on conduction in gases seemed to 

 render it necessary to restrict the term " ionisation " in future 

 to the process of producing atoms differently electrified, and to 

 introduce a new term " electronisation " for the production of 

 conductivity by the motion of particles of apparent mass about 

 1/500 of that of a hydrogen atom. In gases conductivity was 

 probably due to both causes, and in liquids to the former only. 

 In the case of metals, he should like to ask, how thick was the 

 layer of electricity on the surface ? did the thickness of a thin 

 metal plate alter its capacity ? and would the electrons fly to the 

 surface of a metal when it revolved ? He thought the questions 

 still open to discussion might be summarised as follows : — 

 (i) The cause and nature of ionisation. 



NO. 1614, VOL. 62] 



(2) The source of the energy in dissociation in a liquid. 



(3) The cause of the failure of the law of dissociation as the 

 concentration increased. 



(4) The reason for the different rates of migration of the ions, 



(5) The nature of the double layers, or why different metals 

 should attract electricity differently. 



(6) Are the processes of ionisation the same in liquids and 

 gases ? and, if so, why ? 



(7) Do electrons gravitate, i.e. have they a material nucleus 

 or not ? 



(8) Is magnetism due to rotation of the electrons? 



Dr. Larmor, before calling on the chemists present for their 

 remarks, pointed out that the large dielectric constant of water 

 meant a large electric moment for the water molecule, and 

 therefore a considerable separation of the positive and negative 

 charges on the molecule. A molecule of dissolved salt might 

 therefore readily come under the influence of one of these 

 charges alone. 



Prof. H. E. Armstrong stated that in the opinion of chemists 

 the atoms were permanent and stable, and that the removal of 

 1/500 of the mass of a hydrogen atom along with its negative 

 charge seemed to them impossible. He thought that the same 

 process produced conductivity in gases which produced it in 

 liquids ; that in gases the vapour of water played the part of the 

 water in electrolysis of a dissolved salt, and that in all cases it 

 was necessary to form a " tiiplet " by the presence of a third 

 substance, before any chemical or other action could result. This 

 third substance was generally one having one of its constituents 

 in an " unsatisfied " condition, like the oxygen in water or the 

 nitrogen in ammonia, and in which there was in consequence a 

 tendency towards " association " of molecules. 



Mr. Whetham stated by letter that he did not think the diffi- 

 culties of the dissociation theory were as great as they were 

 represented. The ions might be free from each other but be 

 connected with the molecules of the solvent. 



Principal Oliver Lodge thought that although in a liquid the 

 charges apparently travelled with the atoms, while in a gas the 

 electrons appeared to be free, in neither case was conduction by 

 means of molecular aggregates excluded. He considered me- 

 tallic conduction the handing on of the electrons from one atom 

 to another. He looked forward to an electrical theory of 

 matter, in which the hydrogen atom would consist simply of 

 500 electrons without nuclei. 



Mr. W. J. Pope pointed out that the dissociation theory only 

 held up to concentrations of 5 per cent., and that there was a 

 difficulty in the case of salts which on account of their asymmetry 

 rotated the plane of polarisation of light. 



Dr. H. C. Pocklington gave an account of his work on the 

 radiation of a black body on the electro- magnetic theory. As- 

 suming that the energy of the total radiation emitted by a black 

 body at any temperature is the product of powers of the tem- 

 perature 9, the velocity of propagation of the radiation v, and the 

 atomic charge Q, Dr. Pocklington finds by the theory of dimen- 

 sions that the power of the temperature is 4, i.e. Stefan's law, and 

 that the radiation between K and A.-I-SA. is proportional to 



/';-Q-t- /(§)• 



in agreement with Wien's law. 



Mr. C. E. S. Phillips gave an account of his experiments on 

 the apparent emission of kathode rays from an electrode at zero 

 potential. He has found that the green flecks which make their 

 appearance on the inner surface of a partially exhausted vacuum 

 bulb when a discharge passes, are due to the emission from the 

 kathode of jets of occluded gas, which continue even when the two 

 electrodes ot the bulb are both earth connected. These jets 

 produce shadows of opaque bodies held in their path, and 

 although their velocity is probably not greater than that of 

 sound, they can cause the green fluorescence in the glass on 

 which they impinge. 



Mr. J. B. B. Burke communicated a paper on the phosphor- 

 escent glow in gases. He uses electrodeless tubes, and finds 

 that the glow begins to appear at a pressure of ■7 mm., is a 

 maximum at 'I, and disappears at '02 mm. of mercury. It 

 seems to be composed of two parts, one carrying the charge, the 

 other uncharged, but capable of producing conductivity in those 

 parts of the tube to which it penetrates. The conductivity effect 

 is propagated quickly, but the glow appears to be propagated by 

 diffusion along the tube. Prof. A. Smithells mentioned that his 

 experiments on flame showed that the emission of light from 



