14 On the Progressive Increase of Temperature 
stant calms. The vapors raised by the heat of the sun remain suspen= 
ded above the surface of the water, and prevent farther evaporation. 
The sea loses thus less of its aqueous particles, and it is consequently — 
less salt than at 12° N. and 18° S. Lat. In these regions the trade 
winds carry off immediately the vapors formed by the solar heat, — 
which is bere little less than at the equator, and give place to other — 
vapors which rise immediately. In this way evaporation proceeds, — 
and the saltness increases rapidly. This consideration would explain 
also the greater saltness of the western part of the Atlantic Ocean; — 
for we know that the more we approach the coasts of Africa, the — 
more frequent and more continued are the calms. In the South Sea; 
great calms are not experienced towards the east, and hence the —_ E 
gitude has no influence on the saltness of i its waters. ‘2 
Arr. IlI.—Note on the Progressive Increase of Temperature 
descend beneath the surface of the Earth. ce 
From the Ediuburgh Journal of Science for April, 1832. 
Tr is long since the attention of scientific men was first directed — 
to the observation of the high temperatures of mines, and the natural — 
inference it appears to suggest. The deeper the mine, the higher : 
in general is the temperature; and data have been carefully collect- 
ed, and an expression deduced from them, of the rate at which the — 
temperature increases as we descend from the surface into the bowels 
of the earth. The mean rate of i increase, calculated from experi- — 
ments made in six of the deepest coal mines in Durham and Northum- — 
berland, is 1° F. for a descent of forty four English feet. Cordier 
found it in some French mines to increase more rapidly ; and the — 
latest and apparently most carefully deduced result, that of Kupfier,* 
makes the temperature to increase 1° for every 36.81 Er 
But objections of various kinds have been made to this result. 
-have even refused to believe that the high temperature of 
mines i indicates any increase of heat in the centre of the earth. They 
a to discover in the presence of many workmen ‘the — 
candles burned,—in the gunpowder frequently employed fe blasting, 
—and more lately} in the condensation of the air Lo rushing — 
; prs i 
_™ Pog. An. xv. p. 159. ; t Edin. Review, Noveltc® ae 
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