■OF CORNWALL. I03 
attraction of the greater heat within a room or wall, than there is 
on the outfide of the wall. If it be fo hard that it will not admit 
of any water into it’s pores, which is the cafe of fome marbles 
it will however occafion great damps, by condenfing the moifture 
of the air (which would otherwife gently difperfe and vanilh) into 
water, to fuch a degree, that pavements, ornaments and pannels, 
ot fuch marble, ihall fweat (as the ufual phrafe is) and even run 
with water. It being the ufual and juft method to line walls with 
brick, to make the walls wholfome and dry, in order to difcover 
Dy what means bricks obviate damps, I made the following expe- 
riments in July, 1755. I took two bits from off the fame brick, of 
the clofeft and mod uniform texture; N". ,. weighed in air, 31, 
grains ; after it had been immerfed five minutes in water, it weighed 
(after being carefully wiped with a linen cloth) 368 grains, fo that 
it imbibed, by an immerfion of five minutes, 34 grains, which 
to it’s whole is as one-fifth — 22 . 
N'\ 2, weighed in air 326 grains, but after an immerfion of five 
minutes, 392 grains, having imbibed 66 grains ; the fame brick having 
one of it s angles placed contiguous to fome drops of water, fucked 
up ill more; a third fpecimen of like confidence, which had 
not been immerfed at all, on touching fome drops of water fucked 
V m , out i °* immediately. By thefe experiments it is plain, 
that brick does not obviate damps by it’s averfion to, or repulfion 
of water, becaufe it imbibes water more rapacioufly than any ftone. 
I placed therefore both thefe pieces of brick fo charged with 
water, in a South dry window, July i S) 1755, at nine o’clock, 
a. m. ; by twelve at noon N a 1 had evaporated five grains, by half 
paft three, p. m. it had loft five grains more; at five it had rather 
gained than loft (the weather proving rainy) ; by three quarters after 
iix, p. m. it had loft only half a grain in three hours and a quarter, 
the weather continuing, cloudy, with fome rain ; at half hour after 
11 u iV 6 ne rl m0min g> J u ty ^ had loft more, four grains and 
a hall, and by nine, a. m. which compleated the 24 hours, it had 
oit more, xour grains ; fo that in 24 hours this piece of brick had 
evaporated by natural heat, nineteen grains, which, to fifty-four, 
the quantity imbibed is fomewhat more than one third. 
N . 2 had been purpofely for a moment or two, put contiguous 
to water- again, to try ir it would imbibe more moifture than it’s 
immerfion had fupplied it with, and yet in 24 hours, this fpecimen 
evaporated only fixteen grains, viz. one quarter and two fixteenths 
or what it had imbibed. 
So retentive is brick of that moifture which it admits; by which 
it appears that crick obviates damps, not by refifting or defending 
• See Carantoc marble above. 
the 
