1904.] 



Colours in Metal Glasses and Films. 



443 



1. The membrane, owing to the fact that there is no glazed cap to 

 the tube, goes right up to the ends.* 



2. There is no necessity to have pressure-tight joints. 



3. Greater speed in working ; the actual experiment takes from 

 2 to 3 hours only. 



4. The form of tube used is such that it will withstand very high 

 pressures — it may be of interest to mention that one of the tubes and 

 membrane stood a pressure of 120 atmospheres without apparent harm. 



We publish this preliminary notice as it will be some time before 

 the experiments can be continued — a new apparatus has to be cast, and 

 new porcelain tubes are required. We hope, by means of the new 

 apparatus, to reduce greatly the guard-ring leak. 



We are glad to avail ourselves of this opportunity to thank 

 Mr. W. C. D. Whetham for the kindly interest he has taken in the 

 research and Mr. H. Darwin for designing the pressure apparatus. 



** Colours in Metal Glasses and in Metallic Films." By J. C. 

 Maxwell Garnett, B.A., Trinity College, Cambridge. Com- 

 municated by Professor Larmor, Sec. R.S. Received April 

 19 — Read June 2, 1904. 



(Abstract.) 



The first part of the paper is devoted to coloured glasses. The 

 phenomena which it seeks to explain were observed by Siedentopf and 

 Zsigmondy.f Expressions are first obtained for the electric vector of 

 the light scattered from a small metal sphere when a train of plane 

 polarised light falls upon it, the investigation following Lord 

 Rayleigh.J By means of these expressions it is proved, from the 

 diagrams and statements given by Siedentopf and Zsigmondy, that 

 the metal particles which they observed in gold glass are spherical in 

 shape when the diameters are less than 10 -5 cm. The fact that such 

 particles are spherical throws light on the manner in which metals 

 ■crystallise out of solution, the particles taking first a spherical form 

 under the action of surface tension, and later, when they become too 

 large for fche forces of surface tension to overcome the crystallic 

 forces, becoming amenable to the latter. Mr. G. T. Beilby has 

 previously arrived at similar conclusions. § 



An investigation into the optical properties of a transparent medium 



* Cf. Adie, loc. cit. 



f ' Ann. der Phya.,' January, 1903. 



% ' Phil. Mag.,' vol. 44, 1897, and ' Collected Papers,' vol. 4, p. 305. 

 § ' Brit. Assoc. Report,' Southport, 1903. 



