2 SPRINGS, RIVERS, CANALS, LAKES, 



quainted with, rise to the surface of the loftiest mountains, where 

 it is traced so abundantly. And to this hypothesis has consequently 

 been added that of subterraneous heats or fires, by which, the water 

 being rarefied, has been conceived to ascend through the bowels of 

 the mountains in the form of vapours, and to be afterwards con- 

 densed, and once more rendered liquiescent. Yet no sufficient proof 

 has hitherto been offered either of the existence of such subterra- 

 neous fires, or of such cavernous structure, in the mountains sup- 

 posed to be operated upon. 



II. The capillary hypothesis : or that of those who conceive that 

 the water ascends from the depths of the sea through the sandy or 

 other pores of the earth, in the same manner as it rises in capillary 

 tubes, in sponge or sugar-loaf, so long as the latter remains undis- 

 solved. It is, however, sufficient to observe, in confutation of this 

 hypothesis, that though, in consequence of capillary attraction, the 

 water may reach the top or extremity of the hollow sand or minute 

 tube, it will pass no further ; it will neither rise above the surface 

 of the mountain, so as to roll down its lateral surface in torrents, 

 nor constitute cisterns or cavities, in such elevated situations. 



III. The hypothesis of evaporation : or the origin of springs, 

 and rivers from melted snow, rain, dew, and condensed aerial 

 vapours. 



But is the process of evaporation thus contemplated in the aggre- 

 gate, equal to so prodigious nn effect ! and are those countries or 

 places most remarkable for the number and extent of their rivers 

 when evaporation exists in the greatest abundance? 



If we may credit Mr. Williams, the evaporation from the surface 

 of land covered with trees and other vegetables is one-third greater 

 than from the surface of water ; but this has not been confirmed 

 by other philosophers. From his experiments it appears that in 

 Bradford in New England the evaporation during 17/2 amounted 

 to 42.60 inches. But from the way that his experiments were con. 

 dueled, the amount was probably too great. From an experiment of 

 Dr. Watson, made June 2, 1779> after a month's drought, it appears 

 that the evaporation, from a square inch of a grass plat, amounted 

 to 1.2 grains in an hour, or 28.8 in twenty-four hours, which is 

 0.061 of an inch. In another experiment, after there had been no 

 rain for a week, the heat of the earth being 1 10, the evaporation 

 was found almost twice as great, or = 0.108 of an inch in the day: 



