

1894.] On some Phenomena in Vacuum-tabes. 229 



III. " On some Phenomena in Vacuum-tubes." By Sir DAVID 

 SALOMONS, Bart., M.A., V.-P., Inst. Elec. Engrs. Commu- 

 nicated by Prof. D. E. HUGHES, F.R.S. Received April 30, 

 1894. 



Tliis paper is a contribution upon the phenomenon known as striae, 

 or bands, in vacuum tubes. 



As far as I can learn from the sources of information available to 

 me, no one has jet discovered how to produce a predetermined number 

 of bright and dark bands in a tube having an open or free path. 



After a prolonged investigation I have succeeded in producing this 

 result. 



This first step having been attained, it is evident that a number of 

 experiments are available for confirming the theories at present held 

 in regard to the subject, or possibly for modifying existing views, or 

 even to form some additional theory, if necessary, 



I do not think that it would be judicious, at the present stage of 

 my experiments, which are by no means complete, to enter upon 

 any theoretical considerations, although some conclusions might 

 suggest themselves which, however, until the work has been greatly 

 extended, would possibly lead to error. 



It would appear that the main efforts of those experimenting with 

 vacuum-tubes have been in the direction of securing very high ex- 

 haustions and using currents of very high electromotive force. In 

 many cases also currents having a high frequency have been em- 

 ployed. 



When I began these investigations, about twenty years ago, the 

 chief difficulty was to know at what point to commence. After due 

 consideration I decided upon the following course : 



A very large number of vacuum-tubes were " lit up," and all tubes 

 which showed a somewhat similar phenomenon were carefully ex- 

 amined, and their characteristics noted. It is probable that the 

 number of tubes so examined considerably exceeded a thousand, 

 perhaps several thousands. 



At last it became quite clear that, to produce a definite pheno- 

 menon, the tube must be given some definite characteristic ; and 

 having settled this point I was enabled to start upon a systematic in- 

 vestigation. 



There is no object to be gained by detailing the reasons which led 

 me to work in the manner I did, and, therefore, I will be content to 

 give the results. 



When I use the word vacuum-tube I employ it in the ordinary 

 sense. In all the experiments to be described the tubes contain ex- 



