1893.] President's Address. 387 



and Tait,* Kobinson,f Cromwell Varley,^ De la Rue and Muller, 

 Spottiswoode,|| Moulton,^" Grove,** Crookes,ft Schuster,^ J. J. 

 Thomson, and Fleming, |j|| almost a complete history of the new 

 province of electrical science which has grown up, largely in virtue 

 of the great modern improvements in practical methods for ex- 

 hausting air from glass vessels, culminating in Spreiigel's mercury- 

 shower pump, by which we now have " vacuum tubes " and bulbs 

 containing less than 1/190,000 of the air which would be left in 

 them by all that could be done in the way of exhausting (supposed 

 to be down to 1 mm. of mercury) by the best air-pump of fifty years 

 ago. A large part of the fresh discoveries in this province has been 

 made by the authors of these communications ; and their references to 

 the discoveries of other workers very nearly complete the history of 

 all that has been done in the way of investigating the transmission of 

 electricity through highly rarefied air and gases since the time of 

 Faraday. 



Varley's short paper of 1871, which, strange to say, has lain almost 

 or quite unperceived in the Proceedings during the twenty-two years 

 since its publication, contains an important first instalment of dis- 

 covery in a new field the molecular torrent from the "negative 

 pole," the control of its course by a magnet, its pressure against either 

 end of a pivoted vane of mica according as it is directed by a magnet 

 to one end or the other, and the shadow produced by its interception 

 by a mica screen. Quite independently of Varley, and not knowing 

 what he had done, Crookes was led to the same primary discovery, 

 not by accident, and not merely by experimental skill and acuteness 

 of observation. He was led to it by carefully designed investigation, 



* ' Boy. Soc. Proc.,' vol. 10, 1860, p. 274 ; ' Phil. Trans.,' 1860, p. 118. 

 t ' Koy. Soc. Proc.,' vol. 12, 1862, p. 202. 

 i ' Koy. Soc. Proc.,' vol. 19, 1871, p. 236. 



'Koy. Soc. Proc./ vol. 23, 1875, p. 356; vol. 26, 1877, p. 519; vol. 27, 1878, 

 p. 374; vol. 29, 1879, p. 281 ; vol. 35, 1883, p. 292; vol. 36, 1881, pp. 151, 206 ; 

 ' Phil. Trans.,' 1878, pp. 55, 155 ; 1880, p. 65; 1883, 477. 



Jl 'Roy. Soc. Proc.,' vol. 23, 1875, pp. 356, 455; vol. 25, 1875, pp. 73, 547; 

 vol. 26, 1877, pp. 90, 323 ; vol. 27, 1878, p. 60 ; vol. 29, 1879, p. 21 ; vol. 30, 1880 

 p. 302 ; vol. 32, 1881, pp. 385, 388 ; vol. 33, 1882, p. 423 ; 'Phil. Trans.,' 1878, pp. 

 163, 210; 1879, 165; 1880, p. 561. ' 



1 ' Roy. Soc. Proc.,' vol. 29, 1879, p. 21 ; vol. 30, 1880, p. 302 ; vol. 32, 1881, 

 pp. 385, 388 ; vol. 33, 1882, p. 453 ; 'Phil. Trans.,' 1879, p. 165 ; 1880, p. 561. 

 ** ' Roy. Soc. Proc.,' vol. 28, 1878, p. 181. 



ft ' Roy. Soc. Proc.,' vol. 28, 1879, pp. 347, 477 ; ' Phil. Trans.,' 1879, p. 641 ; 

 1880, p. 135 ; 1881, 387. 



ft 'Roy. Soc. Proc.,' vol. 37, 1884, pp. 78, 317; vol. 42, 1887, p. 371 ; vol. 47, 

 1890 ; pp. 300, 506. 



' Roy. Soc. Proc.,' vol. 42, 1887, p. 343 ; vol. 49, 1891, p. 84. 

 1111 ' Roy. Soc. Proc.,' vol. 47, 1890, p. 118. 



