190 



SCIENTIFIC THOUGHT. 



aid of the now well-known vacuum tubes of Geissler, 1 

 of Bonn, began that long series of experiments on the 

 discharge of electricity in rarefied gases, on the influence 

 of magnets upon the course of the luminous rays, and on 

 the spectra of incandescent gases, which subsequently, 

 in the hands of Sir William Crookes 2 in this country, 

 of Hittorf, Goldstein, Elster and Geitel, and of Giese in 

 Germany, and of a great number of other natural phil- 



1 See the Memoir of Pliicker in 

 the ' Annalen der Physik und 

 Chemie' (1857) ; " Ueber die Ein- 

 wirkung des Magneten auf die 

 elektrischen Entladungen in ver- 

 diinnten Gasen " (reprinted in 

 ' Gesammelte wissenschaftliche Ab- 

 handlungen,' vol. ii. p. 475, &c.) 

 Before Pliicker took up the investi- 

 gation with improved means of 

 exhaustion (later perfected by the 

 well-known Sprengel pump), several 

 French experimentalists notably 

 Quet, Gassiot, and Abria had in- 

 dependently marked the difference 

 of the light near the positive and 

 negative poles, mostly in ignorance 

 of the observations recorded by 

 Faraday in his early " Experi- 

 mental Researches," as far back 

 as 1838, 'referring to the "dark 

 discharge." Lord Kelvin, in his 

 Presidential Address before the 

 Royal Society (November 1893), re- 

 fers to the researches of Faraday, 

 and to a long list of contributions 

 to the same subject contained in the 

 Proceedings and Transactions of 

 the Royal Society. Except those 

 of Faraday, they are all later 

 than Pliicker's earliest papers. 

 Lord Kelvin himself says: "Fifty 

 years ago it became strongly im- 

 pressed on my mind that the differ- 

 ence of quality between vitreous 

 and resinous electricity, . . . es- 

 sentially ignored as it is in the 

 mathematical theories . . . with 

 which I was then much occupied 



(and in the whole science of mag- 

 netic waves as we have it now), 

 must be studied if we are to learn 

 anything of the nature of electricity 

 and its place among the properties 

 of matter." Cf. the words of Hit- 

 torf (Pogg. ' Ann.,' vol. cxxxvi. p. 1), 

 quoted by Rosenberger, 'Geschichte 

 der Physik,' vol. iii. p. 778. 



2 The experiments and discov- 

 eries of Sir W. Crookes on " Radiant 

 Matter," beginning with his paper 

 in the ' Transactions ' in December 

 1878, and continued in many sub- 

 sequent communications, as also in 

 his Address before the Brit. Assoc. 

 in 1879, especially his theoretical 

 explanations based upon concep- 

 tions taken from the kinetic theory 

 of gases, made a great sensation and 

 led to much discussion in this coun- 

 try and abroad. The term Radiant 

 Matter was adopted from Faraday 

 (see Rosenberger, loc. cit., vol. iii. 

 p. 779). The corpuscular theory 

 of light was not indeed revived ; 

 but in general, after much criticism, 

 Crookes's views have to a large ex- 

 tent been adopted ; and if not the 

 corpuscular theory of light, cer- 

 tainly that of electricity has been 

 greatly supported by these brilliant 

 experiments. See J. J. Thomson in 

 the Princeton Lectures (1898), p. 

 189 sqq., and Prof. Kaufmann's 

 Address, delivered at the Hamburg 

 meeting in September 1901 (trans- 

 lated in the ' Electrician ' of Nov- 

 ember 8, 1901). 



