3 §4 Mr. cavendish’s Account of 
\ 
any month, corredfed on account of the heat of the 
quickfilver in the tube; that is, to find what would have 
been the mean height, if the quickfilver in the tube had 
been conftantly of a certain given heat. To do this it is 
fuflicient to take the mean height of the barometer, and 
correct that according to the mean heat of the thermo- 
meter; the refult will be exadtly the fame as if each ob- 
fervation had been corrected feparatelv, and a mean of 
the corrected obfervations taken. For example, fuppofe 
it is defired to find what would have been the mean 
height of the barometer in the month of Auguft 1775, 
if the quickfilver during that time had been always at 
50 degrees of heat: the mean of the obferved heights 
is 29,86 inches, and the mean heat of the thermometer 
is 65° or 50+15. The alteration of the height of the 
barometer by 1 5 0 of heat, according to M. de luc’s rule, 
is ,047 inches; confequently, the corredted mean height 
is 29,8 1 3. 
The veffel which receives the rain is a conical funnel, 
flrengthened at the top by a brafs ring, twelve inches in 
diameter. The fides of the funnel and inner lip of the 
brafs ring are inclined to the horizon, in an angle of 
above 65° ; and the outer lip in an angle of above s° 0(a) > 
which are fuch degrees of fteepnefs, that there feems no 
probability either that any rain which falls within the 
funnel, or on the inner lip of the ring, fhould dafh out, 
( a ) To make what is here faid the more intelligible, there is, in fig. 2. 
given a vertical fe&ion of the funnel, abc ;\nd abc being the brafs ring, BA and 
ba the inner lip, and bc and be the outer. 
or 
