TOL. 



Lxr.] 



PHILOSOPHICAL TRANSACTIONS. 



149 



mountain, Mr. B. directed Mr. Flughes to ascertain it in the common method, 

 by examining the (jxW of the mercury in the barometer, at the top, when com- 

 pared with its state at the bottom. Having made this experiment, Mr. H. re- 

 ported that the difference was one inch and-^; which, according to Dr. Halley's 

 method of computation, would give about 450 yards in height, from the adja- 

 cent plain. 



By the following table it will appear, that the quantities of rain, which had 

 fallen in the two rain-gages were weighed 6 several times ; in 3 of which the 

 contents of the upper receiver exceeded those of the lower ; and in the 3 others, 

 the quantity in the lower exceeded that of the upper. On the whole, however, 

 the contents of the lower rain-gage exceeded that of the upper above half an 

 inch. This trifling difference therefore seems to arise from a shower's lasting 

 perhaps a little longer on the bottom of the mountain, and not from any perma- 

 nent cause, as in Dr. Heberden's observations. 



The inference to be drawn however from them seems to be, that the increase 

 of the quantity of rain depends on its nearer approximation to the earthj and 

 scarcely at all on the comparative height of places, provided the rain-gages are 

 fixed at about the same distance from the ground. Possibly also a much contro- 

 verted point between the inhabitants of mountains and plains may receive a solu- 

 tion from these experiments ; as in an adjacent valley, at least, very nearly the 

 same quantity of rain appears to fall within the same period of time as on the 

 neighbouring mountains. 



Note by Dr. Heberden. — It may not be improper to subjoin to the foregoing account, that, in the 

 places where it was first observed tliat a different quantity of rain would be collected, according ai 

 the rain-gages were placed above or below the tops of the neighbouring buildings, the rain-gage be- 

 low the top of the house, into which the greater quantity of rain had for several years been found to 

 fall, was above 15 feet above the level of the other rain gage, which in another part of London wag 

 placed above the top of the house, and into which the lesser quantity always fell. This difference 

 therefore does not, as Mr. Harrington justly remarks, depend on the greater quantity of atmosphere, 

 through which the rain descends: though this has been supposed by some, who haie thence con- 

 cluded, that this appearance might readily be solved by the accumulation of more drops, in a detcent 

 through a greater depth of atmosphere. — Orig. 



