] 02 FRA GMENTS 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 
as 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 had once confirmed the observation of the illustrious 
Alpine traveler. 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 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 
