86 
Great and even troublesome heats are said to have been observed at 
greater depths, and always increasing in proportion to these depths. 
Morinus (de locis subterraneis) relates that in the mines of Hungary, 
which are 5 00 cubits deep, the heat becomes very troublesome when the 
miners get below 480 feet deep. 
The accurate Mons. de Luc in going 1359 feet perpendicular in the 
mines of Hurtz, on July 5, 177^? on a very hot day found the air at the 
bottom warmer than that at top of the shaff. 
Lord Yerulam, and others, have remarked the various temperatures of 
the air in different places of the earth do by no means correspond to what 
should be the result of their position to the sun. 
To omit variations that are small and of less moment, I shall only take 
notice of the much greater cold in all the southern hemisphere than in those 
of the same latitude on the European side of the globe. 
All which seems to argue a copious fund of some other more potent cause 
of heat than the regular action of the sun; and that cause is inherent in the 
earth itself, and is stronger in some regions than in others, though every 
where considerable and of great force. 
Various have been the opinions of philosophers relative to the cause of 
this phenomenon. 
Mons. de Mairon, in a paper published in the Histoire de L’Academie de 
Sciences, in 1/65, has conjectured, that the earth’s internal heat must pro¬ 
ceed from fires kindled within the earth at its center_ 
FirM, from the warm springs found in many parts of the earth, as Bath, 
Aix la Chapelle, which have kept the same temperature at all seasons, and 
through so many centuries.* 
Secondly, the frequent eruptions of burning mountains, which have asto- 
nished mankind through every age. 
Thirdly, the very distant and expeditious communication of the shocks 
of some great earthquakes. 
That of Lisbon in 1755 was perceived even in Scotland and many 
more distant parts. 
These hot springs are always the same; for the longest md <- • 
™ ” * - -* “ 
