$50 POPULAR LECTURES AND ADDRESSES. 



regarding electric sparks, glows, and brushes, and 

 particularly in his " dark discharge " and " dark 

 space " in the neighbourhood of the negative 

 electrode in partial vacuum. In [1523] of his I2th 

 series, he says, " The results connected with the 

 different conditions of positive and negative dis- 

 charge will have a far greater influence on the 

 philosophy of electrical science than we at present 

 imagine." His "dark discharge" ([1544 1554]) 

 through space around or in front of the negative 

 electrode was a first instalment of modern know- 

 ledge in that splendid field of experimental research 

 which, fifteen years later, and up to the present 

 time, has been so fruitfully cultivated by many of 

 the ablest scientific experimenters of all countries. 

 The Royal Society's Transactions and Pro- 

 ceedings of the last forty years contain, in the 

 communications of Gassiot, 1 Pliicker, 2 Andrews and 

 Tait, 3 Robinson, 4 Cromwell Varley, 5 De la Rue 



1 Roy. Soc. Pro,:., vol. IO, 1860, pp. 36, 269, 274, 432. 



a Ibid. p. 256. 



3 //</</, p. 274; Phil. Trans. 1860, p. 118. 



4 Roy. Soc. Proc., vol. 12, 1862. p. 202. 



5 Ibid. vol. 19, 1871, p. 236. 



