eathe would
soon be the financial ruin of a large class of doctors.

CHAPTER VII.

AIR TEMPERATURE.

The most recent definition of heat is that it is a mode of motion; not
movement of a mass of substance, but movement of its ultimate particles.
It has been determined by experiment that the ability of any substance
to absorb heat depends upon the number of atoms it contains, rather than
its bulk or its weight.

It has also been stated that the atmosphere at sea-level weighs about
fifteen pounds to the square inch, which means that a column of air one
inch square extending from sea-level upward to the extreme limit of the
atmosphere weighs fifteen pounds. The density of the air decreases as we
ascend. Each successive layer, as we ascend, is more and more expanded,
and consequently has a less and less number of air molecules in a given
space. Therefore the capacity of the air for holding heat decreases as
we go higher.

We deduce from these facts that the higher we go the colder it becomes;
and this we find to be the case. Whoever has ascended a high mountain
has had no difficulty in determining two things. One is that the air is
very much colder than at sea-level, and the other that it is very much
lighter in weight. We find it difficult, when we first reach the summit,
to take enough of oxygen into our lungs to carry on the natural
operations of the bodily functions. To overcome this difficulty, if we
remain at this altitude for a considerable time, we shall find that our
lungs have expanded, so as to make up in quantity what is lacking in
quality.

If a man lives for a long time at an altitude of 10,000 feet he will
find that his lungs are so expanded that he experiences some difficulty
when he comes down to sea-level. And the reverse is true with one whose
lungs are adapted to the conditions we find at sea-level, when he
ascends to a higher altitude. There is a constant endeavor on the part
of nature to adapt both animal and vegetable life to the surroundings.
While no exact formula has been established as to the rate of decrement
of temperature as we ascend, we may say that it decreases about one
degree in every 300 or 400 feet of ascent. There is no exact way of
arriving at this, as in ascending a mountain the temperature will be
more or less affected by local conditions. If we go up in a balloon we
have to depend upon the barometer as a means of measuring altitude,
which, owing to the varying atmosph