85 
SECT. XVII. 
XII. OF THE EARTH’S INTERNAL HEAT. 
Nymphs ! your fine forms with steps impassive mock 
Earth’s vaulted roofs of adamantine rock; 
Round her still centre tread the burning soil,, 
And watch the billowy lavas as they boil; 
Where in basaltic caves imprison’d deep, 
Reluctant fire in dread suspension sleep; 
Or sphere on sphere in widening waves expand , 
And glad with genial warmth the incumbent land 
So when the mother-bird selects their food 
With curious bill, and feeds her callow brood; 
Warmth from her tender heart eternal springs. 
And pleased she clasps them with extended wings. 
Darwin. 
All the heat we meet with here on the earth we are ready at once to 
ascribe to the action of the sun, overlooking that produced within the earth 
itself, which we shall in this section attempt to shew to be very considerable. 
We learn from the most correct observations, that in the cave of the 
observatory at Paris, only about QO feet under ground, the heat keeps the 
thermometer at 53 ° of Farhenheit; and this without any assistance from the 
sun; it being never sensibly increased by the most scorching seasons one 
degree beyond its heat in the most severe winters that have ever been expe¬ 
rienced there. 
And the same constant and unalterable degree of heat was observed by 
the honourable Mr. Boyle in a cave cut deep into the earth. 
Y 
