83 



few points of the Globe, whether at the surface 

 of the sea, or on the continent*. It is only by 

 the comparison of a great number of observa- 

 tions, made in different parallels of latitude, 

 and at different degrees of longitude, that we 

 shall be able to solve the important problem of 

 the increase or diminution of the heat of the 

 Earth. 



As a preparation for this work, we must care- 

 fully determine, at a given period, the maximum 

 of the temperature of the waters of the sea under 

 the tropics, and in the parallel of the warmest 

 waters. We have proved, that this maximum is 

 at present, in places the most remote from each 

 other, from 28° to 29° of the centigrade thermo- 

 meter. Very distant posterity will one day de- 

 cide, whether, as Mr. Leslie-^ has endeavoured 

 to prove by ingenious hypotheses, two thousand 

 four hundred years are sufficient to augment the 

 mean temperature of the atmosphere a single 

 degree. However slow this increment may be, 



* The currents of the aerial ocean act like the currents of 

 the sea. In Europe, for instance, the mean temperature of 

 a place may augment, because very remote causes make a 

 change in the equilibrium between the winds of the south- 

 west and those of the north-east. We may even conceive a 

 partial change in the mean barometric height of a place, with- 

 out this phenomenon indicating any general revolution in the 

 constitution of the atmosphere. 



+ An experimental Inquiry into the Nature and Propaga- 

 tion of Heat, 1804, p. 181, and 536. 



