] 02 PR A OMENTS OF SCIENCE. 



Newton himself, to prove that the rings were produced by 

 the mutual action in technical phrase, '* interference "- 

 of the light waves reflected at the two surfaces of the film 

 of air inclosed between the plane and convex glasses. The 

 colors of thin plates were "residual colors" survivals of 

 the white light after the ravages of interference. Young 

 soon translated the theory of "fits" into that of" waves;" 

 the measurements pertaining to the former being so accurate 

 us to render them immediately available for the purposes 

 of the latter. 



It is here that Newton's researches and opinions touch 

 the subject of this article. The color nearest to the black 

 spot, in the experiment above described, was a faint blue 

 " blue of the first order" corresponding to the film of air 

 when thinnest. If a solid or liquid film, of the thickness 

 requisite to produce this color, were broken into bits and 

 scattered in the air, Newton inferred that the tiny frag- 

 ments would display the blue color. Tantamount to this, 

 he considered, was the action of minute water-particles in 

 the incipient stage of their condensation from aqueous 

 vapor. Such particles suspended in our atmosphere ought, 

 he supposed, to generate the serenest skies. Newton does 

 not appear to have bestowed much thought upon this sub- 

 ject; for to produce the particular blue 'which he regarded 

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

 quired. 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 England. De 

 Saussure thought that he had actually seen, the cloud-ves- 

 icles, and Faraday, as I learned from himself, believed that 

 he iiad once confirmed the observation of the illustrious 

 Alpine traveler. Dining 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 colors of 

 the sky. The assumption 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 endeavored 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 color of the sky; nor is it neces- 

 sary to impose upon condensing vapor the difficult, if not 



