[BARNES] ANCHOR-ICE FORMATION 93 



On the night between the 31st of December, 1834, and the 1st of 

 January, 1835, after the mean temperature of the air had continued 

 for three da^^s at -47° Falir., and when (here had been little frost in 

 the season l^efore, there cummenced a hard frost, with a calm and 

 perfectly cloudless sky, which continued with little abatement till the 

 5th of January, at 10 a.m. Tn the night between the 3rd and 4th, 

 the temperature of the air was 23" Fahr. ; and on the 4th, the bottoms 

 of the rapids in the Leochal were seen coated in some places with sil- 

 very cauliflower shaped clusters of ground-gru. I neglected at this 

 time to examine the temperature of the M^ater. 



Between the 4th and 5th the temperature was down to 19° Fahr.; 

 and on the 5th I examined the Don and the Leochal along half a 

 mile of each, beginning the examination at half-past eight o'clock a.m. 

 The examination began at the bridge of Alford, built of granite over 

 the Don, in the middle of one of the rapids. At this rapid, the whole 

 bottom, with the exceptions to be immediately stated, was covered with 

 silvery gru, appearing from trvo or three to five or six inches deep. 

 My attention was particularly directed to the exceptions, as throwing 

 a clear light on the question of the radiation of heat from the bottom. 

 Eound each of the piers, and in front of the abutments of the bridge, 

 there was a space quite clear of all frozen matter, excepting at a side 

 of one pier under an arch, where a piece of very still Avater, caused 

 by an obstruction at the bottom, was covered by clear sheet ice. On 

 the south side of the river, two embanking walls, one up and the other 

 down the stream, each twelve yards long, are built in a line with 

 the water courses of the abutment. Close to the bridge these walls are 

 eight feet high from the bottom of the stream, but as they recede from 

 the bridge the masonry slopes gradually to a lower level, till the ex- 

 tremities are little above the level of the -water. The bottoms in front 

 of these walls are clear of ground-gru, as well as that in front of the 

 abutments; but the breadth of the clear space in front of the walls 

 narrowed gradually towards their extremities, in proportion as the 

 masonry became lower, till at the extremity of the downward wall 

 especially, which ends at a sloping gravelly bank, the gru came to 

 the edge of the water. The space of the bottom clear of gru was 

 about five or six feet broad at the high parts of the walls next the 

 bridge; and the water runs on the place at the medium depth and 

 velocity of the rapid. There was another clear space in the bottom of 

 this rapid. About twenty-five yards above the bridge there is, in the 

 middle of the stream, a piece of still water, caused by an elevated bed 

 of gravel, just below it, over which the stream is very shallow. The 

 still water, for an extent of two or three square poles, was covered with 



