Formation of Glaciers. 13 



flowing from under the thick ice ; but just at its exit, not 

 itself covex'ed with ice. The air, at the time, was 30°. These 

 observations require but little comment. I may briefly re- 

 mark, that in the gradual increase of ice, and the reduction 

 of the temperature of the streams in ascending, the tendency 

 appears to glacier formation, to which I have alluded ; and, 

 indeed, the higher tarn may be considered as an approach to 

 a mer de glace ; seeing that the water running into it was 

 only 1° above the freezing-point, and that flowing out only 3° 

 above that point, and about 4° or 5° below that of water of 

 its maximum density. 



That Grasmere should have been almost entirely frozen 

 at this time, whilst the adjoining shallow lake of E-ydal was 

 in great pai't open, I apprehend is to be accounted for, in 

 connection with the property peculiar to water, of being at 

 its greatest density at about 40°, — the latter lake ha\ing for 

 several weeks previously been supplied chiefly with the deep 

 water flowing from the former, little rain having fallen, and 

 comparatively little snow, — the whole quantity at Ambleside, 

 as measured by the rain-gauge during the preceding six 

 weeks, having been only 3.425 inches, of which .745 inch 

 was in snow. The country people, struck with the contrast 

 between the two lakes, accustomed to see the shallower 

 first frozen, attributed the difference to an erroneous cause, 

 viz., to Rydal Lake being less agitated by the wind ; I say 

 erroneous, for even granting that it was more disturbed, of 

 which there is no proof, surely the opposite effect from the 

 agitation might rather have been expected, — a greater reduc- 

 tion of temperature, and a quicker freezing. To those M'ho 

 have given any attention to the subject, it is hardly necessary 

 to observe, that there is no difficulty in explaining the more 

 common occurrence of Rydal Lake freezing first. As soon 

 as its water is reduced to 40°, the first sharp frost must have 

 that eff"ect ; and the heavy rains of the beginning of winter 

 are often nearly as cold as this, not to insist on its constant 

 tendency to this temperature, owing to its connection with 

 the lake of Grasmere. 



I have already mentioned the sudden change of tempera- 

 ture of the tributaries of. the Rotha, on the breaking up of 



