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 here 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 lon- 

 gitude has no influence on the saltness of its waters. 



Art. III. — JVote on the Progressive Increase of Temperature as we 

 descend beneath the surface of the Earth. 



From the Edinburgh Journal of Science for April, 1832. 



It 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 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 Kupffer,* 

 makes the temperature to increase 1° for every 36.81 English feet. 



But objections of various kinds have been made to this result. 

 Some have even refused to believe that the high temperature of 

 mines indicates any increase of heat in the centre of the earth. They 

 have affected to discover in the presence of many workmen, — in the 

 candles burned, — in the gunpowder frequently employed for blasting, 

 — and more latelyf in the condensation of the air constantly rushing 



* Pog. An. XV. p. 159. t Edin. Review, No. ciii. 



