Lesson xxx.j SPRINGS, f03 



time, he took a vessel of water salted to the same 

 degree with that of sea-water, in which he placed 

 a thermometer, and by means of a pan of coals 

 brought the water to the same degree of heat as 

 would be produced by the sun in summer : he 

 then affixed the vessel of water with the thermo- 

 meter in it, to one end of a pair of scales, and 

 exactly counterpoised it with weights on the other. 

 Then, at the end of two hours, he found by the 

 alteration in the weight of the vessel, that a six- 

 tieth part of an inch in the depth of the water was 

 gone off in vapour; and therefore, in twelve hours, 

 one tenth of an inch would have gone off. 



From this experiment the Doctor calculates (in 

 as accurate a manner as the subject will admit) 

 the quantity of water raised by evaporation from 

 the Mediterranean Sea, to be at least five thousand 

 two hundred and eighty millions of tuns of water 

 in a day ; and from the River Thames twenty mil- 

 lions three hundred thousand tuns per day, on the 

 average. If, as it appeared reasonable to conclude, 

 other seas and rivers should afford vapour in the 

 same proportion, when they are acted upon by the 

 sun in a similar degree; or in greater or less pro- 

 portions as they are acted upon in a greater or less 

 degree; this was thought, by the Doctor, a source 

 abundantly sufficient for the supply of Fountains. 



The waters thus raised by evaporation, he ima- 

 gined would keep rising, and float in extremely 

 fcmall and light bubbles, till, being condensed by the 

 cold, they become specifially heavier than the air 

 when they would descend, or being driven by the 



wind* 



