The Republican. [volume] (Oakland, Md.) 1877-current, 1881-08-27
Heat and Humidity.

"How is it that the heat affects us
less on some days with the thermometer
at 80 deg. than on others with the mer-
cury at 50 deg to So deg.P" This is the
question asked by correspondent with
an observing turn of mind, and he refers
to two dates as exemplifying what he
means. These are the 18th and 14th of
.Julv. which we clearly remember
as to their relative comfort and discom-
fort. We might reply to him briefly
that the thermometer does not tell all
the story as to the "bearability" of heat.
Other things come in to ameliorate or to
aoprayate the temperature "a breeze or
quantity of moisture in the air. ''Rela-
tive humidity" however, as you find it
in the weather reports, is the great
helper or the great offender. 1t is less
comfortable on hot moist day than on
hotter dry day.
On Tuesday, July II, the first of the
DAYS mentioned, the maximum temper
ATTIRE Cat the Signal Office) was 80 deg.
and the relative humidity Cor moisture
in the air) ranged from 80 to 100 per
cent. with an effect by no means pleas
ant. 1t was sultry, ''muggy" day,
while on Thursday, the 18th, the Their
mometer rising to much higher point
900 A deg than on the 18th, the hu-
Nudity was much lower, ranging from
81 to Ga per cent only, leaving the heat
much more endurable. This latter day
was in fact a remarkably pleasant day,
though over ten deg. hotter than the
former, and this was not due to q
stronger breeze, as the, Signal Serve
thermometer wind measurer) registered
the same velocity of the winds-from
four to ten miles an hour on both days.
The sensible difference in the two dats,
as respects the comfort of the bodyis,
therefore, traceable to the great hupld-
ity of the air on the 10Th and the smller
degree of moisture on the 18th.
The term "relative humidity, or
humidity" it is true, does not rter to
the absolute quantity of moistureln the
air. In the language of meteorooglsts,
the term humidity denotes ne de-
gree of its approach to saturatin in the
air Cor containing as much 8 it can
hold). 1t expresses the poportion
which the amount of vapor actually
present in the air bears to tht amount
which the air would hold if twas at the
point of Standardization dev, mist or
rain is about to fall from it. When the
humidity is recorded as 10G the air is
completely saturated with Moisture and
rain is imminent, but if re,orted at 70
it contains only three-fouths OF the
amount requisite for satuation. For
tunately for Philadelphian, the average
humidity of the air here YARN and year
out is under 70, and we ar exempt from
the sultry climate of mary places lying
even in higher ATTITUDES.
1t is of great importance for those
who would profit by tie daily Signal
service reports to bearin mind the sig
nificance of its "humdity'' column,
especially in the so-calld /" dog days"
The warmer the air Is the larger be-
comes the quantity of Invisible vapor it
is capable of sustaining and storing
away in the interstces between its
atoms. At the freezing point it can only
hold one one-hundredth part of its own
weight of invisible vapor; at the tenn
perature of SO deg, one'eightieth part of
its weight; at Sc deg, one-fortieth part,
and for every addition of 81 deg. of
temperature it's capacity is doubled. If
fully saturated Mt 80 deg. of tempera-
vapor per cubic foot; at 60 deg, 5.S7
grains in each cubic foot, and at so deg.
of the thermometer 1921 grains. A fall
of temperature from so deg. to GO deg.
throws down therefore nearly 5 grains
of water for every cubic foot of air thus
chilled. A cubic foot of saturated air
under average pressure and tempera-
ture of 80 deg. weighs 495 grains Troy,
of which AS grains are pure aqueous
vapor. With the tenn oerature verging
on 100 deg as it sometimes does in our
"water waves" the atmosphere, at
saturation, contains as much as 10 ga
grains of water to the cubic foot, from
which some idea may be gathered of
the enormous rain fall possibilities of
tropical clouds, which, heated up di-
tectly under the fierce sun, are replete
with evaporation from equatorial seas.
As these watery particles offer resist
ance to the heat of both the earth and
air beneath them, which is seeking to
escape by radiation into the upper at
mosphere, they thus effectually prevent
the cooling of the soil and of the lower
aerial strata. While the .relative hui
midity'' data in the Weather Bureau
bulletins do not give the absolute
amount of vapor in the air, neverthe-
less, when the percentages given are
high, or near 100, they show that the
molecules of vapor are coalescing over
head, and are forming with the air
atoms canopy above us which inter-
cepts the heat of the earth in its attempt
to fly into the clouds. The vapor pres
ent also prevents the body from throw
ing off the high cumulative temperature
thus engendered in our midsummer
weather depends upon several circum-
stances. Evaporation from the skin
and lungs is perhaps the most impor-
tant means the body has of reducing its
surplus heat, as DIR. Max Won Petten-
koffer, the eminent Munich hygienist,
has shown by the use of an apparatus
for testing the quantity of water evap-
GRATED by men and animals. His exper-
iments demonstrate that men at rest
, evaporate about two pounds only during
twenty-four hours, but on day of hard
work four and a half pouads of water.
sin the first instance" he says, 'about
| 2,0l6 caloric units in the second. 4. 4SO
| had m loo va tho hnd,, -, 'L- +.