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the earth. We know it in this way : — The experiments, as with 

 many good experiments, began Avith the French, who fixed 

 thermometers with very long stalks, to the great depth of twenty- 

 five feet into the ground. This was followed up after some time 

 by similar thermometers at the Observatory at Edinburgh, and 

 about the same time at Greenwich, and there the deeper 

 thermometers are read every day. The first and most conspicuous 

 result of this, is the discovery of the retardation of the seasons. 

 High midsummer at a depth of twenty-five feet occurs in 

 December. It has taken five months for the heat at the surface 

 to travel down twenty-five feet. That is very slow travelling. If 

 you compute it further, it takes a hundred years to travel a mile. 

 If the crust of the earth is one hundred miles thick above any of 

 the hot matter which may be supposed to be below it, it must 

 take ten thousand years for the transmission of heat through it, 

 and so on in proportion to the thickness of the crust. This shows 

 that really after all we may have a great deal of heat below us, 

 and it will not come to us for a very long time. It will come at 

 last, but it will be travelling slowly; and in the meantime v/e have 

 the radiation from the earth, so that it is conceivable, with the 

 cool comfortable earth we have here, there may be a great heat 

 below. In every part, I believe, of the earth, there is the evidence 

 of intense heat at former times. The extent of volcanic action is 

 very much disguised on the earth by the effects of air and water, 

 which have degraded the surface in almost every part. The body 

 which is most nearly similar to the earth in some former state, in 

 several respects, is the moon. But the moon has no air and no 

 water. The surface of the moon, in almost every part, is volcanic ; 

 and that would in a former state have been seen on the earth in 

 general ; but in the earth the action of the air and water have 

 degraded the rocks, and many traces of their original form are 

 lost. But if we look at the old rocks of the earth, we find there 

 has been volcanic heat in some shape or other in almost every 

 way. In the limestone rocks, for instance, there are the basaltic 

 beds, which in some places go by the name of "toadstone;" they 

 are certainly the result of volcanic heat which has produced 



