136 FRAGMENTS OF SCIENCE. 



cles suspended in our atmosphere ought, he supposed, 

 to generate the serenest skies. Newton does not ap- 

 pear to have bestowed much thought upon this subject; 

 for to produce the particular blue which he regarded 

 as sky-blue, thin plates with parallel surfaces would be 

 required. The notion that cloud-particles are hollow 

 spheres, or vesicles, is prevalent on the Continent, but it 

 never made any way among the scientific men of Eng- 

 land. De Saussure thought that he had actually seen 

 the cloud-vesicles, and Faraday, as I learned from him- 

 self, believed that he had once confirmed the observa- 

 tion of the illustrious Alpine traveller. During my 

 long acquaintance with the atmosphere of the Alps I 

 have often sought for these aqueous bladders, but have 

 never been able to find them. Clausius once published 

 a profound essay on the colours of the sky. The as- 

 sumption of small water drops, he proved, would lead 

 to optical consequences entirely at variance with facts. 

 For a time, therefore, he closed with the idea of vesicles, 

 and endeavoured to deduce from them the blue of the 

 firmament and the morning and evening red. 



It is not, however, necessary to invoke the blue of 

 the first order to explain the colour of the sky; nor is 

 it necessary to impose upon condensing vapour the 

 difficult, if not impossible, task of forming bladders, 

 when it passes into the liquid condition. Let us ex- 

 amine the subject. Eau-de-Cologne is prepared by dis- 

 solving aromatic gums or resins in alcohol. Dropped 

 into water, the scented liquid immediately produces a 

 white cloudiness, due to the precipitation of the sub- 

 stances previously held in solution. The solid parti- 

 cles are, however, comparatively gross; but by dimin- 

 ishing the quantity of the dissolved gum, the precipitate 

 may be made to consist of extremely minute particles. 

 Briicke, for example, dissolved gum-mastic, in certain 



