200 
Relation of Moisture in Air 
[April, 
some requiring special temperature and moisture condition 
of the air for the work, to which temperature and condition 
the workmen must conform. 
There are three means provided for the healthful disper- 
sion of animal heat into the atmosphere ; the first is 
radiation to surrounding colder objects; the second, con- 
duction to the atmosphere, which, for comfort, must be 
sensibly cooler than the body ; and the third is evaporation 
from the moist surfaces of the lungs, throat, and the roots 
of the pores of the skin. The first of these means, to the 
clothed person at least, is comparatively ineffective, while 
the relative quantities of heat which may be eliminated in 
any given time or locality, by the two last, will probably be 
found nearly equal in an atmosphere of about 70° tempera- 
ture and 65 to 70 per cent, of humidity. In all cases of 
excess of animal heat, the animal, and mankind as an 
animal, find relief in evaporation of water secreted in the 
system, showing that vaporisation is the ultimate means of 
dispersion of heat. 
Even the races of animals exhibit diversity of natural 
methods of dispersing the surplus animal heat. Thus the 
dog obtains relief through the breathing functions, and ex- 
tends the surface of evaporation by exposure of the tongue, 
while the horse breaks out into profuse perspiration of the 
skin. 
The relation of what is indicated by the sense of cold or 
warm to definite temperature with varied proportions of 
humidity may be examined at this stage of the argument. 
Considering a nearly saturated atmosphere, it will be found 
that its effects differ with the temperature altogether. Such 
an atmosphere at from 35° to 50° is found to be intolerably 
chilly, and although evaporation may be checked, and this 
source of loss of heat be removed, yet the conductive and 
radiating value of the vapour in the air is now elevated 
enormously. The cooled surface of the cuticle absorbs the 
natural heat of the skin, and represses the evaporation of 
secretions almost entirely. An aCtual transfer of heat from 
the skin to the vapour in contaCt with the surface occurs, 
the superheated vapour no longer rushes away from the 
skin in search of that vacuum, which is the accompaniment 
of a usually low dew-point, but merely transfers its heat to 
the next particle of cold vapour, which is packed in conve- 
nient juxtaposition to receive it ; or else an aCtual move- 
ment of the heated vapour effects a circulation or current 
which brings a new cold particle to receive a new increment 
of heat. In an atmosphere of this nature the exhaled 
