652 Mr. C. G. Barkla on the Velocity of 



of crystalline matter, and fall off comparatively rapidly with 

 increasing distance. This view is in harmony with the fact 

 that substances which tend to assnme the colloidal condition 

 are in general those which possess feeble powers of crystalliza- 

 tion. A solid colloid is in fact an amorphous body possessing 

 only an exceedingly minute velocity of crystallization. 

 Whether, however, a colloid body is quite analogous to a 

 highly supercooled viscous liquid with excessively small 

 velocity of crystallization, such as " solid " glass, is not a 

 question which I shall attempt to consider here. Some 

 colour, is, however, given to this view by the recent work of 

 Barus, who considers he has obtained colloidal solutions of 

 glass in water. 



The whole question is intimately connected with the 

 hitherto unsolved problem as to the real nature of the solid 

 state. 



Chemical Laboratory, 



University College, London, W., 

 Christmas, 1900. 



LXVI. The Velocity of Electric Waves along Wires. By 

 Ohakles G. Barkla, B.Sc, 1851 Exhibition Scholar, 

 Trinity College, Cambridge*. 



THE theory of the propagation of electric waves along a 

 wire, when a hollow surrounding cylinder serves as the 

 return circuit, was given by J. J. Thomson in 'Recent 

 Researches 'f. 



More recently Sommerfeld % discussed the problem of the 

 propagation of waves along a single wire isolated in space. 

 By the consideration of several examples, the conditions of 

 which may be realized in practice, he showed the velocity of 

 propagation along fine wires to be considerably less than the 

 velocity through free space. 



The propagation of electric oscillations along parallel wires 

 has recently been discussed by Mie § and Morton || . 



Experimentally, Trowbridge and Duane^T found that u the 

 velocity of short electric waves along two parallel wires 

 differs from the velocity of light by less than 2 per cent, of 

 its value/'' (The copper wire used was of diameter *215 cm.) 



* Communicated bv Prof. J. J. Thomson. 



f J. J. Thomson, 'Recent Researches,' p. 262 (1893). 



\ A. Sommerfeld, Wied. Ann. lxvii. p. 283 (1899). 



§ Mie, Ann. d. Phys. ii. p. 202 (1900). 



|| Morton, Phil. Mag. [5] vol. 1. p. 605 (1900). 



1[ Trowbridae & Duanef Am. J. Sc. ser. 3, vol. 1. p. 104 (1895). 



