[barnks] anchor-ice FORMATION 103 



ground, in the middle of a garden, remote from shade, the soil was 

 observed to be frozen to the depth of îout inches, by the clear frost, 

 which had continued from the Ist of January, with the trifling inter- 

 mission above mentioned. On digging into similar ground at the 

 north base of a wall six feet high, the soil was found, close at the 

 foot of the wall, frozen to the depth of only half an inch; at a foot 

 distance from it, about an inch; at two feet, little more; and it was 

 only at the distance o£ ten or twelve feet that it was frozen hard to 

 tlie depth of three inches. A similar modification of the effect of 

 Tiidiation was observed in the shade of trees. Under the Scotch fir 

 tlie soil, slightly covered with decaying herbage, was not at all frozen; 

 nlthough in similar ground, similarly covered, but remote from shade, 

 it was hard frozen to the depth of two or three inches. 



Xow the ground-gni in the rivers was modified in a way strictly 

 similar by the effect of shade. The bridge of Alford, over the Don, 

 is happily situated for illustrating this, being on one of the rapids, 

 where the ground-gru is earliest and most abundantly formed. While 

 the other rapids, and the unshaded parts of tliis one, were quite occu- 

 pied by gru on both the 5th and 7th of January, spaces in the shade 

 of the masonry at this bridge were quite clear of it. It cannot be 

 admitted as an explanation of this fact, that heat may have been there 

 laterally transmitted to the water by contact with the piers and walls; 

 for if this took place, why then did the clear spaces on the bottom 

 narrow gradually towards the low extremities of the embanking walls? 

 Besides, the transmission of heat laterally had not hindered the forma- 

 tion of surface-ice, in contact with a (pier, on a piece of still water 

 "under one of the arches. The modification of the radiation by shade 

 was also exhibited in the absence of all gru on the bottom, along the 

 foot of the dense tuft of Phalaris grass in the Leochal, where there 

 could be no more transmission of heat laterally, than at the general 

 line of the grassy banks of this stream. 



The water, too, returning warmer from under the surface-ice, on 

 the little pools at the edge of one of the rapids, is another instance 

 of the modification of the radiation by shade. The thin white opake 

 covering of hoar frost on the ice prevented radiation, at least in a 

 great measure, and the heat of the bed of the river, in (the course of 

 continual transmission upwards, from strata not yet cooled to much 

 depth by the frost, finding no witlet by the radiation, was expended 

 in heating the water by contact. 



There was another phenomenon observed on the 5th of January, 

 (although no longer seen on the 7th, being then concealed by the 

 immense formation of gru), which can be readily explained by the 



