136 DR. DUFFIELD, MESSRS. BURNHAM AND DAVIS ON THE PRESSURE, ETC. 



loss of an atom of carbon from the cathode was associated with the transfer of four 

 electronic charges between the poles, this favours the ejection of electrons from the 

 atom itself rather than from the pole face considered as a whole, but the writer does 

 not wish to rule the possibility of thermionic emission out of account. 



One point which emerges from the present research deserves mention. After the 

 discovery of the recoil, and during the endeavour to find a means of disentangling it 

 from the electromagnetic effect due to the rest of the circuit, it was suggested that 

 the two might be identical, that is to say, that the mutual interactions between 

 various parts of a circuit were occasioned by the mechanical effect of the flow of 

 electrons through it. It seemed possible to find a plausible explanation of the motion 

 of a movable wire in the plane of a circuit on this basis. The experiments described 

 on pp. 123 and 124 showed that the two exist simultaneously, and that the electro- 

 magnetic effect under the conditions of the experiment was about twice that observed 

 for the recoil. Moreover, the rates of increase of the two with the current strength 

 were different, a fact which effectively disposed of this idea. 



The writer has observed a similar recoil upon the suspended cathode within a 

 highly exhausted vacuum tube, but the mechanical effect has not yet been 



measured. 



The experiments were conducted in the Physics Laboratory of University College, 

 Reading, and valuable assistance was given by Mr. J. S. BURGESS. Mr. DAVIS was 

 in receipt of a Research Grant from the Committee of the Privy Council for Scientific 

 and Industrial Research, to whom the thanks of the authors are accorded. 



