ON BODIES SMALLER THAN ATOMS. 325 



from the previous experiment the value of vm/e, we deduce the value of 

 m/e. The value of m/e found in this way was about 10~", and other 

 methods used by Wiechert, Ivaufmann and Lenard have given results 

 not" greatly different. Since m/e = 10~'^, we see that to carry unit 

 charge of electricity by the particles forming the cathode rays only re- 

 quires a mass of these particles amounting to one ten thousandth of a 

 milligram while to carry the same charge by hydrogen atoms would 

 require a mass of one-tenth of a milligram.* 



Thus to carry a given charge of electricity by hydrogen atoms re- 

 quires a mass a thousand times greater than to carry it by the nega- 

 tively electrified particles which constitute the cathode rays, and it 

 is very significant that, while the mass of atoms required to carry a 

 given charge through a liquid electrolyte depends upon the kind of 

 atom, being, for example, eight times greater for oxygen than for 

 hydrogen atoms, the mass of cathode ray particles required to carry a 

 given charge is quite independent of the gas through which the rays 

 travel and of the nature of the electrode from which they start. 



The exceedingly small mass of these particles for a given charge 

 compared with that of the hydrogen atoms might be due either to the 

 mass of each of these particles being very small compared with that of 

 a hydrogen atom or else to the charge carried hy each particle being 

 large compared with that carried hy the atom of hydrogen. It is there- 

 fore essential that we should determine the electric charge carried by 

 one of these particles. The problem is as follows: suppose in an en- 

 closed space we have a number of electrified particles each carrying 

 the same charge, it is required to find the charge on each particle. It is 

 easy by electrical methods to determine the total quantity of electricity 

 on the collection of particles and knowing this we can find the charge 

 on each particle if we can count the number of particles. To count 

 these particles the first step is to make them visible. We can do this 

 by availing ourselves of a discovery made by C. T. E. Wilson working 

 in the Cavendish Laboratory. Wilson has shown that when positively 

 and negatively electrified particles are present in moist dust-free air 

 a cloud is produced when the air is closed by a sudden expansion, 

 though this amount of expansion would be quite insufficient to produce 

 condensation when no electrified particles are present: the water con- 

 denses round the electrified particles, and, if these are not too numer- 

 ous, each particle becomes the nucleus of a little drop of water. Now 



* Professor Schuster in 1889 was the first to apply the method of the 

 magnetic deflection of the discharge to get a determination of the value of 

 m/e; he found rather widely separated limiting values for this quantity and 

 came to the conclusion that it was of the same order as in electrolytic solutions, 

 the result of the method mentioned above as well as those of Wiechert, Kauf- 

 mann and Leonard make it very much smaller. 



