Year: 1865

The evidence of design is enforced when
we consider how exactly the density of the
atmosphere has been adjusted to the hu~
man organism. By density is meant the
quantity of matter the atmosphere con-
tains in given volume for example, in
cubic yard. This quantityis capable of
exact measurement; aud it is found that,
at the level Of the sea, one cubic yard of
the atmosphere, when dry, contains about
two pounds Of air. This weight is the
measure of its density. Now, We find that
the organization of plants and animals,
including man, has been most skilfully
adjusted to the density of the air. Ac,
cepting the fact for the present as granted,
let US consider the conditions on which
this adaptation of the air to our physical
organization rests. s..-. --.


The density of the atmosphere depends
on four eonditions;-First, on the inber-
ent nature Of the substance which we call
airitself; secondly, on theinteUsity ofgra7-
ity-that is, on the amount of the earth's
attractive power; thirdly, on the total guam
tity of air oh the globe; and lastly, on the
temperature. The influence of the first
condition is not at present understood,
but thatof the last three we can readily
trace. If the intensity of the force of
gravity at the surface of the earth were to
change, other circumstances remaining the
same, the density of the atmosphere would
change in the same proportion. Thus,
fer example, if the intensity Of gravity on
the earth were as great as 1t is Oh the sur
face of the sun, the density Of the atmos-
phere would be twenty y-eight times as great
as at present. Or if this intensity were
reduced to that which exists on the surface
of the moon, the density would be dimin-
ished to onessixth Of its present degree.


But assuming that the intensity of the
force Of gravity on the surface of fthe earth
remained constant, precisely the same ef-
feet would result from any variation in the
total quantity of the atmosphere. Were
the whole amount of air on the earth in
creased or diminished, the density of the
atmosphere at its surface would also be in
creased or diminished in tie same proper
ton. Still further, assuming that, while
the intensity of the gravity and the mass
of the atmosphere remained fixed, the tenn
perature were changed, then also the den
sity of the atmosphere would vary, and by
a quantity which can easily be determined
By accurate experiments it has been as,
certaiRed that an elevation of temperature
equivalent to about five hundred degrees
of our Fahrenheit thermometer would re-
ducs the density in the same proportion.
Now, consider what all these relations
imply. When we reflect that the eintensity
of the force of gravity depends upon the
mass of the earth, and remember that the
mean temperature depends upon the
distance of the earth from the sun, we see
that not only the actual size of the earth,
but also its distance from the sun, and the
quantity of air on its surface, were all
necessary conditions, in order that the
atmosphere should have its present density
and thus become the it abode of man. II
any one of those conditions had been
neglected, the result would not have been
attained, and man as be exists, could not
have lived on this globe,