DECEMBER. 
389 
in spring, when its purpose is answered^ and when it would 
be no longer an advantage but an encumbrance^ it is shed in 
thick matted masses^, and got rid of by rubbing, &c. the coat 
becoming thin and smooth as before. A similar change takes 
place in those animals which are clothed with fur in sum- 
mer ; on the arrival of cold weather^ the base of the fur is 
filled with a very thick and soft down, like that of birds, which 
disappears in spring, as may be seen in the hare^ racoon, &c. 
It is the same if we alter the climate of any animal : the 
hair of the dog becomes wool or fur in very cold climates^ 
and the wool of the sheep becomes hair in torrid ones. It is 
this circumstance that makes the furs of cold regions so much 
more valuable than those of warmer ones ; the texture is 
thicker^ softer, and more downy ; the same species which 
produces fur at Hudson's Bay producing little else than hair 
at the Gulf of Mexico. 
C. — Here is a caterpillar of the Buff leopard Moth 
( Arctia Isabella J, coiled up in an auger-hole in this maple 
tree : he too is probably protected from the cold by his tufts 
of thick bristly hair. 
F, — Perhaps so : and yet I am not quite certain that 
animal heat is generated by insects, or that they need exter- 
nal covering. — All the operations of agriculture have now 
ceased : the digging out of the potatoes was the last of the 
processes belonging to the crops of last season ; which was 
generally completed two or three weeks ago. The potato is 
perhaps the greatest blessing which America has given to 
the world ; its consumption is already spread over the civil- 
ized world, and its cultivation is yearly extending, on both 
continents. 
C. — After the potatoes are stored, you begin to plough 
for next year. 
F, — Yes, and before : immediately after harvest, we 
plough at intervals when the weather will not admit of any- 
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