177 
to the dryness of Davos ; and many of the medical writers 
on Davos have been misled in the same way, and give 
examples which have nothing to do with the dryness of the 
climate, for instance, the sun shining on the dark roofs or 
road makes the surface on which it shines extremely warm, 
and as the warm layer of air is capable of containing much 
more moisture than the colder air above, the evaporation is 
extremely rapid, and the roof or road is soon dried, and the 
moisture rises into a colder air, in fact sometimes this 
stratum of air is so much colder than that below that it 
cannot contain as much moisture as exists in the warmer 
air, and the banks are seen to steam, showing that the 
ground is warmed by the sun, but by itself not giving any 
clue as to the amount of moisture in the air. These 
phenomena, or the rapid drying of ink, or cracking of furni- 
ture, have often been used to illustrate the dryness of 
climates, whereas they really, in such cases, only show the 
difference of temperature of the room and outside air or the 
warming of the ground ; but these considerations show us 
that the physiological action of the dryness or dampness of 
a climate is not a simple one, for as the body is warmer 
than the surrounding air evaporation must take place more 
rapidly from the skin than from the evaporometer, and the 
difference will be more marked, cceteris paribus, when the 
quantity of absolute moisture is small, that is, when the air 
is cold. 
In the same way cold air entering the lungs is raised to a 
temperature approaching blood heat ; now this cold air may 
be relatively moist, but the absolute moisture which it con- 
tains is but small, so that when raised to nearly blood heat it 
would be very dry, which means that it can absorb a great 
deal of moisture, which will be the case, and it will carry 
off a large quantity from the lungs. An example will make 
this clearer. Supposing that the air breathed at the sea 
level is 20° F., and contains 80 per cent of the possible 
