532 Mr. Jackson on the Method of Transmission of 



these particles of excited activity would collide with the 

 molecules of the gas in which they are produced, and it is 

 suggested that in a certain percentage of these collisions a 

 negative particle is expelled, leaving the excited activity 

 positively charged. To explain the results obtained in this 

 investigation on this view, it is necessary to assume that the 

 particles of excited activity, when mixed with air at 1 cm. 

 pressure, travel a distance comparable with 1 cm. before 

 becoming charged. This distance is great compared with 

 the mean free path of a molecule of air at the same pressure, 

 and therefore only a very small fraction of the collisions 

 can be effective in causing a negative particle to be expelled 

 by the excited activity. 



I am indebted to Professor Schuster both for placing the 

 resources of his laboratory at my disposal and also for much 

 valuable criticism during the course of these experiments. 



LX. Note on a Paper by W. Makower entitled " On the 

 Method of Transmission of the Excited Activity of Radium 

 to the Cathode.'' By W. H. Jackson, M.A., Assistant 

 Lecturer hi Mathematics in the University of Manchester*. 



AS a result of some experiments on the method of trans- 

 mission of the excited activity of radium, Mr. Makower 

 has arrived at the following hypothesis : — The molecules of 

 excited activity, initially uncharged, are projected from radium 

 emanation with velocities large compared with those of gas 

 molecules, and at a certain percentage of encounters with the 

 gas molecules a negative electron is shot off, leaving the 

 activity positively charged. 



It gives additional force to his argument to further show 

 that the deviation of the experimental results obtained by him 

 from those required by the above theory are actually less 

 than the errors of observation. 



Since the number of ions present in a gas ionized by a small 

 quantity of radium emanation is exceedingly small compared 

 with the number of molecules of gas, it is safe on this view, 

 even though the positive ion influences a much larger field of 

 force than an ordinary molecule, to assume that the importance 

 of encounters with positive ions is negligible. 



The amount of activity which, in the experiments described 

 b} r Mr. Makower, is deposited on the cathode, is to be taken 

 proportional to the number of excited activity molecules 



* Communicated by the Physical Society. 



