Evening star. [volume] (Washington, D.C.) 1854-1972, 1931-07-23
BY THOMAS r.. HENRY.

"It's not the heat It's the humidity. "
Such is the curbstone explanation of
the unusual discomfort folk experience
these hot July days.
Next Winter the same persons will
declare that it isn't the cold, but the
humidity that makes them suffer.
Both these explanations are quite
true SO far as they co. says DR.. William
j. Humphreys of the Weather Bureau.
But this same humidity" Is one OF
the trickiest subjects that the meteorol-
ogist deals with and in the final an
alysis nobody knows just why the
amount of water vapor in the air should
act on the human system as 1t un-
doubtedly does.
The greater the saturation of the
atmosphere close to the earth the less
can be evaporated from the surface OF
the skin. 1t requires heat to change
water-in this case the water in sweat
from a liquid into vapor. The heat
is supplied by the body If the water
isn't evaporating the heat Is not needed.
1t stays with the body. That's why
one feels hotter when the humidity is
high.
MetabOliSm a Factor.
But heat is produced in the body by
the action of metabolism. There is a
good deal of evidence, DR.. Humphreys
says, that this metabolism itself is partly
function of temperature. The hotter
it gets on the outside the lower the
metabolism, and consequently the less
j heat produced inside Consequently the
| less the evaporation from the skin the
less heat there is to be gotten rid of
The two processes, however, may not
balance.
/ But the lower the metaboliSm the
| less heat energy is present for throw
| ing of the waste products of the body
and so, it is possible, poisons accumu-
| late and the individual feels sluggish
and downcaSt. And. of course, the
metabolism can't be allowed to get toe
low If it does the heat-producine
! living itself drops too low and the
victim dies. Atmosphere at the water
| vapor saturation point at tempera-
| ture of 100 degrees Fahrenheit. DR.
Humphreys believes, would be fatal tC
man If continued for any length OF
time. Such a condition would be
practically impossible in nature.
1t is this sluggishneSS produced by
| the lowering of metabolism in response
to the greater accumulation of heat
outside, unrelieved by the evaporation
conception that humid air is heavier
than dry air. AS a matter of fact. DR.
Humphreys says, it is lighter. Water
vapor itself is lighter than dry air
per unit volume. The person feels
heavier. Everything around him seems
to have taken on extra weight.
Humid Air Colder.
But humid air is less comfortable in
Winter. 1t makes a person feel colder
This also is due to the fact that the
atmosphere laden with water vapor
does not take up moisture so readily
from the surface of the skin. The re-
suit probably is that the clothing be-
comes damp, although not necessarily
enough so to notice it. Damp cloth
ing is a better conductor of heat than
dry clothing. So the heat produced
by the body has a better chance to
escape. The metabolism may not be
able to increase fast enough to conpen-
safe in heat production.
1t is notable, DR.. Humphreys points
out, that in dry, cold air the skin on
exposed parts CT the body has a scaly,
mealy appearance, while on a day of
high humidity it is moist and of a
greater compactness throughout it's
thickness. The dry, mealy skin Is a
poor conductor of heat away from the
body The wet skin may take it away
too fast for an exact balance to be
maintained.
The physiology of humidity, DR.. Hum
phreyS explained still is quite obscure,
although the main fact-that of its
effect on evaporation from the skin sur