Middletown transcript., 1898-08-20
WHAT HUMIDITY rs.

| WHAT HUMIDITY IS.
The ''humidityn Is reported in {
weather bulletin on a certain day to be
95 percent. Everyone gathers from thil
that the air is excessively charged will
moisture, and everyone knows, too, thai
this circumstance has quite as much tC
do with the oppressiEehess of the wea.
ther as does the temperature as shown
blythe thermometer. But how many per
sons can say precisely what is meant by
a humidity Of 95 or any other per cent?
Here is in substance, weather mans
Interpretation of the figures:
The air always contains more or less
moisture, since water evaporates and
mingles with it in the form Of invisible
vapor even at the lowest temperature.
The amounG of vapor, which the air can
contain varies with its temperature.
At low temperature it can hold in
suspension smaller amount of water
vapor then when it is highly heated.
When the air is charged with the full
amount Of vapor which at its tempera-
ture it can hold it is said to be !, satu-
rated. Evaporation then stops, and il
the temporal ure fall, however slightly,
the air must necessarily give up por-
tion of its charge of vapor, which may
form into droplets and gather into clouds
or it may be deposited in the form Of
dew. Here is the explanation of the film
of moisture which we sometimes see
gather upon an ice-pitcher in a warm
and close room. The layer of air immed
late contact with the pitcher has be-
come too cold to retain all of its mois-
ture has been cooled below the "dew
point"-aLd the surplus of vapor is de-
posted on the glass or metal.
The figures which are given out by the
Weather Bureau indicate only what is
called "relatiye humidity" That is to
say, they indicate not the actual amount
of water vapor in the air at any given
time, but the degree Of the airs ap-
proach to saturation. Complete satura-
tion is represented by the figures 100
and air absolutely free frem vapor by 0,
though the latter state Of things never
occurs, humidity as low as 10 being
rarely found even in the most arid re-
gions. In this way of reckoning, hui
midity of SO per cent. means that the
ircontains just one-half Of the amount
Of vapor which would saturate it at the
existing temperature. While the hu-
midity stands at this figure, evaporation
will 60 on rapidly, and since the evap-
Grafton Of the moisture of our bodies
tends to keep us cool, we experience no
sense of expressiv heat even though the
thermometer stands high. With hui
midity rs per cent. which may be brou-
ght about either by fall Of temper
ature while the amount of moisture in
The air remains the same, or by any in
crease in the amount of moisture, the
temperature remains unchanged, evap-
Grafton becomes less rapid, and when
the figures 80 ard upward are reached
it nearly ceases; and if at the sans time
the temperature fairly high, the moist
ure which ooZes from our pores remains
upons us, and we sweater as in a
steam bath.
The instrument used for ascertaining
the humidity of the air is known as the
There are several sorts of
hygrometers in use, the most common
being the " dry and wet bulb hygrome-
ter" The esential parts Of this in
strument are two thermometers, of
which one registers the temperature Of
the air in the ordinary way, while the
other, which has it's bu lb covered with
q piece Of muslin kept continually 4
moistened with water, indicates low |
or temperature caused by the cooling Of |
its bulb by evaporation. The less
moisture there is in the air the more |
rapid will be the evaporation from this
wet bulb and the greater the fall Of the
mercury in it's tube. This instrument /
therefore indicates only rapidity of |
but this having been as
certained, the percentage of humidity |
can bs got at in roundabout way by
means Of an algebraic formula, or as is
lone in practice, from table prepared
sor the urpose, which gives the !" dew
point" corresponding with the reading
If the hygrometer at different tempera-
;ure.