28 ROUND THE YEAR 



covered the ground with a thick and solid frozen 

 mass. The birds strayed in great numbers into the 

 valley of the Wharfe, and were found in the culti- 

 vated fields along the river. Many were said to be 

 injured by dashing against the telegraph wires. 1 



THE DEPTH TO WHICH THE GROUND FREEZES. 



Jan. 9. A question came up to-day which I was 

 unable to answer off-hand. This is our first winter in 

 a new house, and the domestic management wants to 

 know whether our water-main, which lies about 2 ft. 

 6 in. below the surface of the ground, is liable to 

 freeze. I have never had occasion to consider this 

 question, and was, at first, unable to give a clear 

 answer. By and by it occurred to me that the insect 

 larvae, which winter in the ground, are often found 

 less than a foot deep. It seems probable, therefore, 

 that frost does not usually penetrate to the depth of 

 one foot. 



Jan. ii. Mr. G. J. Symons, F.R.S., who has made 

 long and careful observations of underground tem- 

 perature, gives me in a letter received this morning 

 some interesting particulars. " The earth," he says, 

 " at one foot below its surface very rarely reaches 32 

 F. Here (Camden Square, London) it fell to 32*2 

 on Jan. 6 and 7, 1893, and to 32 on Jan. 29, 31, and 

 Feb. i to 5, 1880. It did not fall to 32 here in 1875, 

 but it just reached it at the gardens of the Royal 

 Botanic Society, Regent's Park, on Jan. i, 2, 3 and 4, 



1 Zoologist, March, 1886, 



