Formation of Ground-ice. 7 



at 42° ; and in a room without a fire, at 60°. Viewed in re- 

 gard to protection from the influence of radiation, there was 

 reason, it must be admitted, in the old style of laying out 

 gardens, and especially in terraces ; the trimly cut hedge, 

 the formally cut yew tree, the intersecting alleys, all con- 

 duced not only to break the force of the blast, but also to 

 keep the temperature of the air, and especially of the ground, 

 and of the plants themselves, above the freezing-point in the 

 critical time of early vegetation ; and whilst thus protecting, 

 obstructing as little as possible sunshine. 



2. A curious and rather rare phenomenon, that of ground-ice, 

 or a formation of ice at the bottom of streams, contrary to the 

 ordinary law of the freezing of water at the surface, has 

 been happily explained as an effect of radiation, it never 

 having been known to occur, excepting under circumstances 

 specially favourable to the radiation of heat.* As these ge- 

 nerally are of common occurrence in the lake district, parti- 

 cularly as regards perfect clearness of the streams in fine 

 weather rivalling the clearness of the atmosphere, I expected 

 to learn that this appeai-ance of ice is well known to the na- 

 tives ; but to my repeated inquiries, I always received an 

 answer in the negative ; no one, even those most familiar 

 with the country, had, that they were aware, ever wit- 

 nessed, or even heard of it. And, till this spring, my ex- 

 perience was similar ; I had looked for it in vain. It was 

 on the morning of the 13th of March that I first saw it, after 

 a night, as shewn by the preceding observations, of great 

 cold, the radiating thermometer at 3 A. M. having been so low 

 as 14°. At 11 o'clock in the forenoon, when it was still as 

 low as 25° in the shade, though as high as 52° in the sun- 

 shine on the grass, I examined the state of the two tribu- 

 taries of the Rotha, the principal stream of the valley, and 

 which, flowing from lakes, is almost constantly, even in the 

 severest weather, free from ice, and that even when its pa- 

 rent lakes are entirely covered with ice. The tributaries, 

 on the contrary, descending from mountain valleys, are 



* See the very valuable paper of the Rev. James Farquharson, F.R.S., on 

 this subject, in the Phil. Trans, for 1835. 



