ependent of mechanical
difficulties, two great impediments will forever prevent the realization
of any such ambitions aspirations. These are the increase of cold and
decrease of pressure in the upper regions of the air, and the deficiency
of oxygen in the rarefied element for the support of animal life. It is
well known that at the earth's surface, the pressure on all parts of the
body, internal and external, by the weight of the superincumbent
atmosphere, is no less than 141/2 pounds to every square inch. The
structure of the human body is physiologically conformed by nature to
this pressure, and it cannot survive with any very great change of this
amount, either by increase or diminution. When one descends into the
water, the pressure is doubled at about 32 feet of depth. In ascending
in the atmosphere, the pressure is diminished much less rapidly, of
course, but quite sensibly when the altitude becomes very great.

Messrs. Coxwell and Glaisher are said to have ascended in 1862 to a
height of seven and a half miles. One of these gentlemen became entirely
insensible from cold and want of oxygen, and the other very nearly so,
being obliged to open the valve of the balloon with his teeth for want
of the use of his hands.

Nature provides a partial remedy for the difficulty of breathing in the
upper regions of the atmosphere. In the effort to breathe, the lungs are
found to expand and to develop air cells not ordinarily used, so as to
bring a larger quantity of the rarefied air into contact with the blood.
It has been proposed to assist this effort of nature, and, in order to
enable the aeronaut to reach a greater altitude with safety, to carry up
in bags a supply of oxygen for breathing. As air is carried or forced
down into the water to enable the diver to breathe, so it may be
conveyed upward for the benefit of the aerial adventurer.

But with all possible expedients, it is not probable that man will ever
be able to get far away from the surface of the earth which is his
natural place of abode. If he can explore the lower strata immediately
adjoining his own theatre of action--the strata in which all the great
and important phenomena of meteorology take place--and if he can succeed
in traversing it at his pleasure with safety and some degree of
celerity, as we doubt not he will eventually, this great achievement
will subserve all the useful purposes possible to be derived from such
skill and knowledge.

The atmosph