192 Natural Historij. 



Besides forming and giving to the world this 

 ingenious theory ot evaporation, M. De Luc has 

 also rendered essential service to the science of 

 meteorology, by his patient and persevering ob- 

 servations on the comparative degrees of moisture 

 in the atmosphere, in different situations. On this 

 subject he has brought to light a number of facts 

 equally new and interesting. His countryman, M. 

 De Saussure, has also laboured very successfully 

 in the same field of inquiry;'^ and though not al- 

 ways with an entire coincidence of opinion and 

 result, yet with sufficient agreement on most im- 

 portant points. There are probably no two indi- 

 viduals to whom the scientific world is more in- 

 debted for the minuteness, the accuracy, and the 

 success of their meteorological investigations, than 

 to these philosophers of Geneva. 



About the year 1755 Mr. Eeles first suggested 

 the probable influence of EkctricUi/ in the process 

 of evaporation. He taught that there was but 

 one way of altering the specific gravity of the par- 

 ticles of water, so as to render them lighter than 

 air, and, consequently, buoyant in that fluid, viz. 

 the adding to each particle a sufficient quantity of 

 some fluid which possesses much greater elasticity 

 and rarity than air. Such a fluid is Klectricity ; 

 which, therefore, he supposed to have a very im- 

 portant agency in the ascent of vapours. The in- 

 fluence of the electric fluid in producing changes 

 in the atmosphere has been since further investi- 

 gated, and the principles on which it operates more 

 satisfactorily developed, by Franklin, De Saus- 

 suRE, Bertholon, and other modern inquirers. 



Closely connected with the doctrines which 

 have been taught on the subject of evaporation 

 are the several theories of llain to which modern -v 



d Essai sur VH^gromctrk^ 4to. 1 783, 



