VOL. Lxvix.j Vhilosophical transactions. 141 



and south-west winds are so often accompanied with rain ; for as the air sweeps 

 along the warmer latitudes, it involves a larger proportion of moisture, which 

 is constantly and copiously exhaling from the ocean ; and this moisture being 

 retained in a state of solution till it reaches the colder climates, is then either 

 collected in the clouds or immediately precipitated in rain, according to the 

 different conditions of the atmosphere. 



These foreign supplies however are uniformly restored to the sources from 

 which they were derived : for that proportion of rain which rises not in vapour, 

 after moistening and refreshing the earth, forms springs, brooks, and rivers, and 

 is thus perpetually returning to the ocean whence it was taken ; so truly philoso- 

 phical are the words of the preacher, when speaking of this vast circulation : 

 " All the rivers run into the sea, yet the sea is not full : unto the place from 

 whence the rivers come, thither they return again." 



5. About a century ago, the ingenious Mr. Townley, of Tovvnley, in this county, 

 made some accurate observations on the depth of rain which fell annually in the 

 neighbourhood of the hills which divide Lancashire and Yorkshire; and on taking a 

 medium of 15 years, he determines it to be 4 1.51 6 inches. The depth of rain 

 therefore at Townley, exceeds the depth of rain at Liverpool, about 4 inches. 

 This is probably however less than the real difference ; for there was a source of 

 error in Mr Townley's experiments, with which the world was not at that time 

 acquainted. Mr. Townley's rain-gage was fixed full 1 yards above the surface 

 of the earth ; which circumstance, according to some later observations, makes 

 a very material difference in the result of the experiment. Were the observa- 

 tions to be repeated at Townley, and the rain-gage placed on the ground, there 

 can be no doubt but that the depth of rain would considerably exceed 4l.5l6 

 inches ; for I find from a great number of experiments, made during the last 

 3 years, with 2 vessels of equal dimensions, one placed on the ground, and the 

 other 1 8 yards higher on the battlement of the hospital ; that the quantity 

 received in the lower vessel exceeds that in the higher more than one-third and 

 less than one-half. 



6. An ingenious friend, on perusing these observations, asked, " Whether 

 the fact of evaporation going on equally well in an exhausted receiver, was not 

 an unsurmountable objection to that theory concerning evaporation, which 

 supposes a chemical solution of water in air ?" With a view to ascertain this 

 fact I made the following experiment : Two china saucers, each containing 3 

 ounces of water, were accurately weighed. One of them was placed in the 

 open air ; the quicksilver in the thermometer during the experiment between 

 48° and 50°, the day tolerably clear with a moderate breeze. The other was 

 put under t.^ receiver of an air pump ; the air was exhausted, and the pistons 

 occasionally worked, to draw off any of the water which might be supposed to be 



