KIDD’S VIKW OF THE PHYSICAL CON DITION OF MAN. 
413 
jistance ; an.l though the hurricane may want 
colour, we often fatally experience that it does 
not want force. We have equal experience 
of the air’s spring or elasticity ; the bladder, 
when pressed, returns again, upon the pres- 
sure being taken away ; a bottle, when filled, 
often bursts, from the spring of air which is 
included. 
So far the slightest experience reaches ; 
but, by carrying experiment a little further, we 
learn that air also is heavy; a round glass 
vessel being emptied of its air, and accurate- 
ly weighed, has been found lighter than when 
it was weighed with the air in it. Upon 
computing the superior weight of the full ves- 
sel, a cubic foot of air is found to weigh 527 
grains, while the same quantity of hydrogen 
weighs no more than 40 grains. 
From this experiment, therefore, wm learn, 
that the earth, and all things upon its surface, 
are every way covered with a ponderous 
fluid, which, rising very high over our heads, 
must be proportionally heavy. For instance, 
as in the sea a man at the depth of twenty feet 
sustains a greater weight of water than a man 
at the depth of but ten feet, so will a man at 
the bottom of a valley have a greater weight 
of air over him than a man on the top of a 
mountain. 
If by any means we contrive to take away 
the pressure of the air from any one part of 
our bodies, we are soon made sensible of the 
weight upon the other parts, d hus, if we 
clap our hand upon the mouth of a vessel from 
whence the air has been taken away, there 
will be air on one side and none on the other ; 
upon which we shall instantly feel as if the 
hand were violently sucked inwards, which is 
nothing more than the weight of the air upon 
the back of the hand that forces it into the 
space which is empty below. 
As by this experiment we perceive that the 
air presses with great weight upon every 
thing on the surface of the earth, so by other 
experiments we learn the exact weight with 
which it presses. First, if the air be exhaust- 
ed out of any vessel, and this vessel be set 
with the mouth downwards in water, the wa- 
ter will rise up into the empty space, and fill 
the inverted glass — for the external air will, 
in this case, press up the water where there 
is no weight to resist, as one part of a bed 
being pressed makes the other parts that have 
no weight upon them rise. In this case, as 
we said, the water being pressed without, will 
rise in the glass, and would continue to rise 
thirty-two feet high. From this therefore 
we learn, that the weight of the air which 
presses up the water is equal to a pillar or 
column of water which is thirty-two feet 
high, as it is just able to raise such a column, 
and no more. In other words, the surface 
of the earth is everywhere covered with a 
weight of air, which is equivalent to a cover 
ing of thirty two feet deep of water, or to a 
weight of twenty-nine inches and a half of 
quicksilver, which is known to be just as 
heavy as the former. 
It is easily found, by computation, that to 
raise water thirty- two feet will require a 
weight of fifteen pounds upon every square 
inch. Now, if we are food of computations, 
we have only to calculate how many square 
inches are in the surface of an ordinary, human 
body, and allowing every inch to sustain fif- 
teen pounds, we may amaze ourselves at the 
wmight of air we sustain. It has been com- 
puted, and found, that our ox’dinary load of air 
amounts to within a little of forty thousand 
pounds ! 
The elasticity of the air is one of its most 
amazing properties, and to which it should 
seem nothing can set bounds. A body of air, 
that may be contained in a nut shell, may 
easily, with heat, be dilated into a sphere of 
unknown dimensions. On the contrary, the 
air contained in a house may be compi’essed 
into a cavity not lai’ger than the eye of a 
needle. In short, no bounds can be set to 
its confinement or expansion, at least experi- 
ment has hitherto found its attempts indefi- 
nite. In every situation it retains its elasticity, 
and the more closely we compress it, the more 
strongly does it resist the pressure. If to 
the increasing the elasticity on one side by 
compression, we increase it on the other 
side by heat, the force of both soon becomes 
irresistible ; and Monsieur Amontons sup- 
posed that air, thus confined and expanding 
was sufficient for the explosion of a woidd. 
ON THE 
ADAPTATION OF EXTERNAL NATURE 
TO THE 
PHYSICAL CONDITION OF MAN. 
When Hamlet, in contemplating the 
grandeur of creation, breaks forth into that 
sublime apostrophe on man : “How noble 
in reason 1 how infinite in faculties ! in form 
and moving, how express and admirable I in 
action, how^ like an angel I in apprehension, 
how like a God! the beauty of the world! the 
pai’agon of animals !” who does not feel ela- 
ted by the description ? who does not feel 
conscious of its truth ? 
Nor is its truth the less admissible, be- 
cause the poet, in concenti’ating the powers 
of his imagination on the excellences of that 
work of creation which bears the stamp of 
the Creator’s image, has omitted to pi'e- 
sent to our view the reverse of the impres- 
sion, the frailty namely of our fallen nature ; 
for although, on moral and religious consi- 
deration, each individual is bound habitu- 
ally to take the one view in conjunction with 
the other; in a simply philosophical con- 
templation of human nature, we are not pre- 
cluded by any reasonable bai'rier, from tak- 
ing such a partial view of the subject as the 
occasion may suggest. 
In the present instance, indeed, I am 
strictly called upon to consider, not the 
moral, but the physical condition of man : 
