460 Remarks on the 
subterranean temperature does not arrive at a 
minimum before the end of March; which is 
three months later than the coldest weather 
above ground. 
The facts just stated throw much light on 
the subject of the present essay, by pointing 
out the reason which determines animals of 
known lethargic habits to form their winter 
retreats near the surface of the ground. 
This choice exposes them, according to the 
experiments of Dr. Hales, to a variable tem- 
perature, which ‘sinks slowly at first, and 
keeps them benumbed by a sleepy torpor ; 
but after the rigours of winter are past, the 
hiding places of these slumberers are gradu- 
ally warmed by the returning sun, which 
reanimates their torpid limbs, and _ recalls 
them from their secret dens, at the proper 
moment for ther appearance above ground. 
Had the hedgeliog, the field-mouse, &ce. 
made a contrary choice, and retired to ca- 
verns 80 feet deep, all the benefit they could 
have derived froth an invariable temperature, 
would have consisted, in the certainty) of not 
being frozen; for the same. degree of cold - 
which disposes them to sleep im autumn, 
would evidently perpetuate. their slumbers 
in these situations; unless we suppose them te 
be roused to action by the calls of hunger; 
