of Wells and Springs in Jamaica. 6r 
about London are either of no great depth, or are full of 
water, which are both confiderable objections to their giving a 
mean temperature. The want of depth will make them fub- 
jeCt to the variations of the feafons ; and a large quantity of 
water, even in a deep well, will take the temperature of the 
air more or lefs : for any change of temperature communi- 
cated at the furface will, from the fluidity of the water, be 
readily diffufed through the whole. I fufpeCt it is owing to 
this caufe, that the wells in the neighbourhood of Brighthelm- 
flone vary from 50° to 52°, for thofe were the higheft that 
had molt water in them. My obfervations were made in fu ai- 
mer. Thefe wells are of various depths, from 15 to 150 feet. 
That which I always found the coldeft is not more than 
22 feet deep; I never found its heat greater than 50°. It is 
near the beach, and is a tide well, that is, the water in it 
rifes and falls, and in fo doing does not correfpond exaClly 
with the tides, but follows them with an interval of about 
three hours. At the lowed there is not more than a foot of 
water in it ; and it may be confidered as a fubterraneous fpring 
running through the bottom of the well. There are in faCt 
numerous fprings that break out upon the fand, a few feet 
above the low-water mark, which are doubtlefs the fame that 
fupply the wells. As we are not acquainted with any caufe 
that produces cold in the bowels of the earth, we mud necef- 
farily in every climate, confider the loweft degree of heat as 
approaching neared to the mean temperature ; and therefore 
we cannot conclude the mean temperature at Brighthelmftone 
to be more than 50°. The mean temperature of London is 
computed about 52** ; but Brighthelmftone is nearly fifty miles 
farther fouth than London, and is immediately upon the fea, 
* Kirwan’s Temperature of different Latitudes, p. 73. 
and 
