226 Mr Chree, On some experiments on [June 1, 



ascribes to a species of diffuse reflexion at a bend in a narrow 

 part of the tube. Perhaps this is immediately connected with 

 another phenomenon he observed \ viz. that if the vacuum tube 

 be of variable section then a place where in passing from cathode 

 to anode there is a sudden large increase in the diameter takes 

 upon itself the functions of a secondary cathode, dominating the 

 character of the striae on the side next the anode and emitting 

 molecular streams along the axis of the tube. 



The view that phosphorescence is due to the impact of finely 

 divided matter torn off the cathode by the current has been 

 maintained by Puluj 2 and others, but it seems obviously in- 

 applicable to the phosphorescence proceeding from a secondary 

 cathode, or to that called in by the positive column. Even as 

 concerns the ordinary phenomena some experiments devised by 

 Crookes 3 seem very adverse to Puluj's view. It is, however, 

 unquestionable that cathodes of most substances have matter 

 torn off by the discharge, and that it is frequently largely de- 

 posited on those portions of the tube where the ordinary phos- 

 phorescence is most conspicuous. Messrs Spottiswoode and 

 Moulton 4 have pointed out other resemblances between the action 

 of the molecular streams and that of matter such as lamp-black 

 actually projected from the cathode. 



As regards the function of the molecular streams in the 

 discharge no final results have been obtained, though much 

 speculation exists. Messrs Spottiswoode and Moulton give as 

 the result of their investigations: — "At present we have come 

 to no definite conclusion . . . , but we cannot say that we are 

 aware of anything that conclusively shows that they (the mole- 

 cular streams) have any definite electrical function to perform 

 in the discharge," 1. c. p. 650. " The most attractive hypothesis re- 

 lating to their functions is that they officiate at the birth of the 

 discharge and enable it to get into the gaseous medium...," 

 1. c. p. 651. 



From the remainder of their cautiously worded remarks, I 

 believe Messrs Spottiswoode and Moulton would regard the 

 function ascribed to the molecular streams by this " attractive 

 hypothesis " to be that of carriers of a convective discharge out 

 into the gas. A slight modification would however adapt the 

 hypothesis to the very suggestive views of Messrs E. Wiedemann 

 and H. Ebert 5 . 



1 Wied. Ann. 11, 1880, p. 836, and Ann. 12, 1881, p. 276. 



2 Wiener, Sitzungsberichte, Bd. lxxxi., Abth. n., 1880, pp. 864 — 923, see specially 

 p. 873. 



3 Journal of Electrical Engineers, Vol. xx., Feb. 1891, pp. 29 — 36. 



4 Phil. Trans. 1880, pp. 582 and 649—650. 



5 Wied. Ann. 35, 1888, pp. 217 and 258—9. 



