162 
About thirty years later the idea of put- 
ting condensed air to this use spread from 
France to other countries of Europe, and 
the largest institution of this kind at pres- 
ent is at Reichenhall, the property of E. 
Mack, in which 53 persons can make use of 
the heightened pressure at the same time. 
In 1841 M. Triger, a civil engineer, in- 
troduced in France the idea of using a 
heightened atmospheric pressure in build- 
ing sub-aqueous works, and this gave an 
opportunity to observe what effect an at- 
mospherie pressure which was much higher 
than that of a pneumatic cabinet would 
have upon the workmen. The work under 
pressure is carried on in an iron shaft, the 
sides and top of which are air-tight. It is 
sunk to the bottom, like a diving-bell, while 
the upper end protrudes above the surface 
of the water. The fresh air which is con- 
tinuously pumped in from above expels the 
water below, leaving the bottom free to be 
worked upon. The shaft sinks deeper and 
deeper as the earth is removed, until there 
may be a pressure of 34 or nearly 4 atmos- 
pheres. A pressure of ten meters of water 
is equal to about one atmospheric pressure. 
The effect of the condensed air upon the 
laborers was found to be surprisingly favora- 
ble up to a pressure of two atmospheres. 
The hard work was accomplished more 
easily and with less fatigue than in the open 
air, and in such exertions as running up a 
ladder they did not get out of breath. Even 
after working hours the men felt stronger 
and in better spirits. 
But when the pressure exceeds that of 
two atmospheres the men begin to have 
certain unpleasant sensations, such as itch- 
ing and pains and swelling of those muscles 
which are strained the most. These symp- 
toms donot, however, appear while under the 
heightened pressure, but make themselves 
felt during the time that the men are under 
the normal pressure, and pass away again 
as they return to their work. The over- 
SCIENCE. 
[N.S. Von. VI. No. 135. 
seers are exempt from these effects. They 
receive instead a mental stimulus which 
is manifested by an increased impulse to 
talk. 
If the atmospheric pressure is still further 
increased, the resistance against exhalation 
becomes stronger. The action of the re- 
spiratory apparatus is weakened by the in- 
creased distension of the lungs until it final- 
ly becomes almost imperceptible ; speech is 
difficult, and whistling impossible. The 
result of the too rapid contraction of the 
lungs under a diminished pressure which 
prevents whistling is the same as that which 
follows when the egress of the air expelled 
by the lungs is delayed. 
The enlivening influence on the workmen 
is diminished as soon as the pressure ex- 
ceeds that of three atmospheres. The slow 
and imperfect performance of the respira- 
tory function begins to have a detrimental 
effect upon the gaseous interchange which 
takes place in the lungs by causing the 
carbon dioxide to be retained in the blood. 
The laborers become more easily fatigued, 
and a decrease of appetite is followed by 
loss of flesh, if they continue the work. 
We find, therefore, that there is a limit to 
the condensation of air which a man can- 
not overstep without detriment to himself, 
but there is a wider limit in this direction 
than in that of rarefied air. 
Experience proves that a temporary 
change from the normal pressure to an 
increased or diminished pressure is pleas- 
ant and also benefits vitality in various 
ways. We are able to ascend to any 
altitude at which the air is rarefied to the 
desired degree, but the privilege of choos- 
ing a denser atmosphere in which to live 
is denied us. It is only from a few places 
at very high elevations that convalescents 
can be sent down to a lower altitude where 
they quickly recover by inhaling air which is 
more condensed and contains a larger pro- 
portion of oxygen. The inhabitants of the 
