1897.] on Cathode Bays. 431 



arc charged particles moving with high velocities, that the size of 

 the carriers must be small compared with the dimensions of ordinary- 

 atoms or molecules. The assumption of a state of matter more finely 

 subdivided than the atom of an element is a somewhat startling one ; 

 but a hypothesis that would involve somewhat similar consequences 

 — viz. that the so-called elements are compounds of some primordial 

 element — has been put forward from time to time by various chemists. 

 Thus, Prout believed that the atoms of all the elements were built up 

 of atoms of hydrogen, and Mr. Norman Lockyer has advanced weighty 

 arguments, founded on spectroscopic consideration, in favour of the 

 composite nature of the elements. 



Let us trace the consequence of supposing that the atoms of the 

 elements are aggregations of very small particles, all similar to each 

 other ; we shall call such particles corpuscles, so that the atoms of 

 the ordinary elements are made up of corpuscles and holes, the holes 

 being predominant. Let us suppose that at the cathode some of the 

 molecules of the gas get split up into these corpuscles, and that these, 

 charged with negative electricity and moving at a high velocity, form 

 the cathode rays. The distance these rays would travel before losing 

 a given fraction of their momentum would be proportional to the 

 mean free path of the corpuscles. Now, the things these corpuscles 

 strike against are other corpuscles, and not against the molecules as 

 a whole ; they are supposed to be able to thread their way between 

 the interstices in the molecule. Thus the mean free path would be 

 proportional to the number of these corpuscles ; and, therefore, since 

 each corpuscle has the same mass to the mass of unit volume — that 

 is, to the density of the substance, whatever be its chemical nature 

 or physical state. Thus the mean free path, and therefore the co- 

 efficient of absorption, would depend only on the density; this is 

 precisely Lenard's result. 



We see, too, on this hypothesis, why the magnetic deflection is 

 the same inside the tube whatever be the nature of the gas, for the 

 carriers of the charge are the corpuscles, and these are the same 

 whatever gas be used. All the carriers may not be reduced to their 

 lowest dimensions; some may be aggregates of two or more cor- 

 puscles ; these would be differently deflected from the single corpuscle, 

 thus we should get the magnetic spectrum. 



I have endeavoured by the following method to get a measure- 

 ment of the ratio of the mass of these corpuscles to the charge 

 carried by them. A double cylinder with slits in it, such as that 

 used in a former experiment, was placed in front of a cathode which 

 was curved so as to focus to some extent the cathode rays on the 

 slit ; behind the slit, in the inner cylinder, a thermal junction was 

 placed which covered the opening so that all the rays which entered 

 the slit struck against the junction, the junction got heated, and 

 knowing the thermal capacity of the junction, we could get the 

 mechanical equivalent of the heat communicated to it. The deflec- 

 tion of the electrometer gave the charge which entered the cylinder. 



