ARTIFICIAL SKY. 109 



The latter also underwent slow but incessant modifica- 

 tion. It first resolved itself into a series of strata re- 

 sembling those of the electric discharge. After a little 

 time, and through changes which it was difficult to 

 follow, both clouds presented the appearance of a series 

 of concentric funnels set one within the other, the 

 interior ones being seen through the outer ones. Those 

 of the distant cloud resembled claret-glasses in shape. 

 As many as six funnels were thus concentrically set 

 together, the two series being united by the delicate 

 cord of cloud already referred to. Other cords and 

 slender tubes were afterwards formed, which coiled 

 themselves in delicate spirals around the funnels. 



Rendering the light along the connecting-cord more 

 intense, it diminished in thickness and became whiter ; 

 this was a consequence of the enlargement of its par- 

 ticles. The cord finally disappeared, while the funnels 

 melted into two ghost-like films, shaped like parasols. 

 They were barely visible, being of an exceedingly deli- 

 cate blue tint. They seemed woven of blue air. To com- 

 pare them with cobweb or with gauze would be to liken 

 them to something infinitely grosser than themselves. 



In all cases a distant candle-flame, when looked at 

 through the cloud, was sensibly undimmed. 



2. ON THE BLUE COLOUR OF THE SKY, AND THE 

 POLARISATION OF SKYLIGHT. 1 



1869. 



After the communication to the Eoyal Society of 

 the foregoing brief account of a new Series of Chemical 

 Reactions produced by Light, the experiments upon 



1 In my * Lectures on Light ' (Longmans), the polarisation of 

 light will be found briefly, but, I trust, clearly explained. 



