NA TURE 



[January 30, 1896 



be restricted to a condition in which the components of 

 a molecule are in no way connected by chemical bonds ; j 

 the possibility of the independent diffusion of the mole- 

 cular components through porous membranes would i 

 afford a simple test as to whether molecules were really 

 dissociated or not. The term dissociation as applied to 

 electrolytes, in which this independence of the ions does 

 not exist, is obviously a misnomer. There is said to be 

 an electrical force acting between the various oppositely 

 charged ions into which a dissolved molecule separates, 

 which in some way still binds them. Even in dilute 

 solutions this force is very considerable, and must make 

 the condition of charged ions moving independently in 

 the liquid so unstable as to be dynamically impossible 

 unless other important forces operate at the same time. 

 Although the present theory of free ions affords a rough 

 working analogy, yet it is illusory and misleading, and 

 threatens to prevent important advances by its illusive , 

 appearance of explanation. It must not be forgotten 

 that the older theories of light and the caloric theory of 

 heat constituted stumbling-blocks long after their in- I 

 adequacy had been conclusively demonstrated. 



Prof. Fitzgerald thus contends that the fundamental 

 conceptions underlying many of the current physico- 

 chemical theories, such as those of osmotic pressure 

 and electrolytic dissociation, are dynamically unsound, I 

 so that all attempts to gain an insight of what occurs in 

 solution by their aid are necessarily unsuccessful. He 

 seems to consider that an unyielding adhesion to these 

 theories has led to an illogical habit of thought upon such 

 matters, and has made possible the inaccurate applica- 

 tion of thermo-dynamical reasoning. W. J. P. 



NEW EXPERIMENTS ON THE KATHODE 

 RA YS> 



(i) 'T^WO hypotheses have been propounded to explain 

 ■*■ the properties of the kathode rays. 

 Some physicists think with Goldstein, Hertz, and 

 Lenard, that this phenomenon is like light, due to vibra- 

 tions of the ether,- or even that it is light of short wave- 

 length. It is easily understood that such rays may have 



whether it is the only hypothesis that can do so. Its 

 adherents suppose that the kathode rays are negatively 

 charged ; so far as I know, this electrification has not 

 been established, and I first attempted to determine 

 whether it exists or not. 



(2) For that purpose I had recourse to the laws of in- 

 duction, by means of which it is possible to detect the 

 introduction of electric charges into the interior of a closed 

 electric conductor, and to measure them. I therefore 

 caused the kathode rays to pass into a Faraday's cylinder. 

 For this purpose I employed the vacuum tube represented 

 in Fig. I. A K c D is a tube with an opening a in the centre 

 of the face B c. It is this tube which plays the part of a 

 Faraday's cylinder. A metal thread soldered at S to the 

 wall of the tube connects this cylinder with an electro- 

 scope. 



E F G H is a second cylinder in permanent communica- 

 tion with the earth, and pierced by two small openings at 

 ^ and y ; it protects the Faraday's cylinder from all 

 external influence. Finally, at a distance of about o'lom. 

 in front of F G, was placed an electrode N. The electrode 

 N served as kathode ; the anode was formed by the pro- 

 tecting cylinder E F G H ; thus a pencil of kathode rays 

 passed into the Faraday's cylinder. This cylinder in- 

 variably became charged with negative electricity. 



The vacuum tube could be placed between the poles of 

 an electro-magnet. When this was excited, the kathode 

 rays, becoming deflected, no longer passed into the Fara- 

 day's cylinder, and this cylinder was then not charged ; 

 it, however, became charged immediately the electro- 

 magnet ceased to be excited. 



In short, the Faraday's cylinder became negatively 

 charged when the kathode rays entered it, and only when 

 they entered it ; the kathode rays are then charged with 

 7tegative electricity. 



The quantity of electricity which these rays carry can 

 be measured. I have not finished this investigation, but 

 I shall give an idea of the order of magnitude of the 

 charges obtained when I say that for one of my tubes, at 

 a pressure of 20 microns of mercury, and for a single 

 interruption of the primary of the coil, the Faraday's 

 cylinder received a charge of electricity sufficient to raise 

 a capacity of 600 C.G.S. units to 300 volts. 



a rectihnear path, excite phosphorescence, and affect 

 photographic plates. 



Others think, with Crookes and J. J. Thomson, that these 

 rays are formed by matter which is negatively charged 

 and moving with great velocity, and on this hypothesis 

 their mechanical properties, as well as the manner in 

 which they become curved in a magnetic field, are readily 

 explicable. 



This latter hypothesis has suggested to me some ex- 

 periments which I will now briefly describe, without for 

 the moment pausing to inquire whether the hypothesis 

 suffices to explain all the facts at present known, and 



^ Translation of a paper by M. Jean "Perrin, read before the Paris 



cademy of Sciences on December 30, 1895. 



- These vibrations might be something different from light ; recently M. 

 Jaumann, whose hypotheses have since been criticised by M. H. Poincar^ 

 supposed them to be longitudinal. ' 



NO. 1370, VOL. 53] 



(3) The kathode rays being negatively charged, the 

 principle of the conservation of electricity drives us to 

 seek somewhere the corresponding positive charges. I 

 believe that I have found them in the very region where 

 the kathode rays are formed, and that I have established 

 the fact that they travel in the opposite direction, 

 and fall upon the kathode. In order to verify this 

 hypothesis, it is sufficient to use a hollow kathode 

 pierced with a small opening by which a portion of 

 the attracted positive electricity might enter. This 

 electricity could then act upon a Faraday's cylinder 

 inside the kathode. 



The protecting cylinder E F G H with its opening ^ 

 fulfilled these conditions, and this time I therefore 

 employed it as the kathode, the electrode N being the 

 anode. The Faraday's cylinder is then invariably 

 charged with positive electricity. The positive charges 



