USEFUL PROJECTS. | 
‘distinctly ; and having taken care 
‘to place the jar upon a table near 
the window, in a very favourable 
Tight, I set myself to observe the 
appearances which should take place, 
‘with all that anxious expectation 
which a conviction that the result 
of the experiment must be decisive, 
‘naturally inspired. 
I was certain that the air con- 
‘tained in the bottle could not part 
with its heat, without at the same 
time (that is to say) at the same 
Moment, and in the same place, 
parting with a proportion of its wa- 
ter; if, therefore, the beat pene- 
trated the mass of air from the 
centre to the surface, or passed 
through it from particle to particle, 
in the same manner as it is probable 
that it passes through water, and all 
unelastic fluids, by far the greatest 
part of air contained in the bottle 
would part with its heat, when not 
actually in contact with the glass, 
anda proportional part of its water 
being let fall at the’ same time, and 
in the same place, would necessarily 
descend in the form of rain: and, 
though this rain might be too fine 
tobe visible ia its descent, yet I 
was sure I should find it at the bot- 
tom of the bottle, if not in visible 
drops of water, yet in that kind of 
veloudy covering which cold glass 
acquires from a contact with hot 
steam or watery vapour. 
Bat if the particles of air, instead 
of communicating their heat from 
one to another, from the centre to 
the surface of the bottle, each in 
its turn, and for itself, came to the 
surface of the bottle, and there de- 
posited its heat and its water, I con- 
eluded that the cloudiness occasion- 
ed by this deposit of water would 
‘appear all over the bottle, or, at 
!, mot: more of it at the bot- 
Ais 
411 
tom than at the sides, but rather less; 
and this ‘I found to be the case in 
fact. 
The cloudiness first made its ‘ap- 
pearance upon the sides of the bot- 
tle, near the top of it; and from 
thence it gradually spread itself 
downwards, till, growing fainter ‘as 
it descended lower, it was hardly 
visible at the distance of half an 
inch from the bottom of the bottle; 
and upon the bottom itself; which 
was nearly flat, there was scarcely 
the smallest appearance of cloudi- 
ness. 
These appearances, I ‘think, are 
easy to be accounted ‘for. The air 
immediately in contact with the 
glass being cooled, and having de- 
posited a part of its water upon the 
surface of the glass, at the same time 
that it communicates to it its ‘heat, 
slides downwards by the sides of the 
bottle, in consequence of its “in- 
creased specific gravity ; and, taking 
its place at the bottom of the bottle, 
forces the whole mass of hot air up- 
wards: which, in its turn, coming 
to the:sides of the bottle, there de- 
posits its heat and its water; and 
afierwards bending its course down- 
wards, this circulation is continued 
till all the air in the bottle has ac- 
quired the exact temperature of the 
water in the jar. 
From hence it is clear why the 
first appearance of condensed ‘va- _ 
pour is near the top of the bottle, 
as also why the greatest collection 
of vapour is in that part, and that 
so very small a quantity of it is 
found nearer the bottom of the 
boitle. 
This experiment confirmed ‘me 
in anopinion which I had for some 
time entertained, that, though the 
particles of air individually, or each 
for itself, are capable ‘of Wace 
an 
