1896.] Professor Fleming on Electric Research, 239 



WEEKLY EVENING MEETING, 



Friday, June 5, 1896. 



The Eight Hon. Loed Kelvin, D.C.L. LL.D. F.R.S. Vice-President, 



in the Chair. 



Professor J. A. Fleming, M.A. D.Sc. F.R.S. M.BJ. 



Electric and Magnetic Besearch at Low Temperatures, 



During the last four years much time has been spent by Professor 

 Dewar and by me in the prosecution of a joint research on the 

 principal electric and magnetic properties of metals at very low- 

 temperatures. Some reference has already been made in previous 

 discourses by Professor Dewar to portions of this work,* but the 

 special object of the present lecture is to extend these descriptions, 

 and put you in possession of the latest results in this department of 

 the low temperature investigations. It will be convenient to discuss 

 the several divisions of it in the order in which they have engaged 

 our attention. 



One hundred and sixty-seven years ago Stephen Gray, a pensioner 

 of the Charterhouse, in conjunction with his friend Granvile Wheler, 

 stretched a packthread 300 feet long over silk supports, and demon- 

 strated that an electrification of the thread at one end spread instantly 

 over the whole mass, but that if metal wires replaced the silk no 

 electrification of the thread was possible. This experiment undoubtedly 

 formed the starting-point for the first definite recognition of the 

 necessity for a classification of bodies into insulators and conductors, 

 a distinction which Gray's brilliant contemporary, Dufay, extended 

 and confirmed, and for which he and Desaguiliers coined these familiar 

 terms.j Gray's contributions to knowledge as an epoch-making 

 discoverer have received less notice from scientific historians than 

 their real value deserves. It is less easy to state who first noticed 

 that the powers of conduction and insulation were greatly affected by 

 temperature. Cavendish, in 1776, however, was perfectly familiar 

 with the fact that solutions of common salt conduct electricity better 

 when warm than when cold,J and made measurements of the relative 



* ' Scientific Uses of Liquid Air.' A Friday Evening Discourse, by Pro- 

 fessor J. Dewar, LL.D. F.K.S. delivered at the Eoyal Institution, Jan 19, 1894. 



t See the 'Intellectual Rise in Electricity,' by Park Benjamin. Stephen 

 Gray's papers on this subject, communicated to the Eoyal Society, are as follows : 

 Phil. Trans. 1720, vol. xxxi. p. 104; 1731, vol. xxxvii. p. 18; 1732, vol. xxxvii.' 

 p. 285 ; 1735, vol. xxxix. p. 16 ; 1736, vol. xxxix. p. 400. See also Dufay, Phil 

 Trans. 1733, No. 431, p. 258. 



X See the ' Electrical Researches of Cavendish.' Edited by Clerk-Maxwell 

 p. 324. 



