Lawrence democrat. (Lawrenceburg, Tenn.) 1884-1925, 1891-03-13

the air temperature, no matter what hot
bodies in the vicinity are striving to
make 1t blunder.
The heat radiated by these bodies to
the Thermometer will be carried off by
the wind as fast as 1t arrives. In the
absence of a natural gale, it is only neces-
ary to create an artificial one with q
bellows or fan.
But 1t evidently does not matter
whether the air moves rapidly across
the thermometer or the latter moves
rapidly through the air, and hance it
suffices to attach the instrument to a
short cord and swing 1t rapidly around
in circle.
This arrangement is called "sling
thermometer" some form of which is
generally used for measuring air-tem-
peratures accurately.
A few simple experiments with a
cheap house-thermometer-I say a
''cheap" one; because it is just possible
| that it may be smashed at the beginning
of the experiments-will show the sur
prising effect of rapid motion through
the air.
On hot summer day the thermom-
eter, hanging on sunny porch, may
stand at 1870 degrees. Of course the air
has no such high temperature as this,
and if you take down the thermometer
and hang 1t up in the shade it will grad
uany come to nearly the true tempera-
ture of the air-perhaps 80 degrees or
90 degrees. This descent of the mercury
will take long time, but If in.
stead Of simply hanging the ther-
mometer up you tie string to II
and whirl 1t violently around your
head 1t will reach its final temperature
in very few minutes. Even If the
whirling is done in sunshine and with
great rapidity the direct effect of the
suns rays will be very small and the
instrument will soon record (very near.
ly) the temperature Of the air at that
place, which may on calm day be lit
tie lighter than that of the air in the
shade.
Even thermometer which hangs
constantly in shaded place, far from
any very hot or very cold bodies, does
not as rule correctly indicate the tenn
perature of the air at the time of obser
vation. For the temperature of the all
is almost continually changing-at
times very rapidiy-and the thermome
ter, as is evident from what has beer
said, will not follow these changes al
all closely unless the wind is blowing
hard.
Within doors, too, and especially IL
winter, the temperature Of the air may
change rapidly, and the heat radiatet
from human bodies, lamps and stoves
affects the thermometer.
In all cases, therefore, the sling
method must be used, if we wish t.
know the true temperature of the air,
But, 1t may be asked, why confine ou
attention to the temperature Of the ar
The suns rays, the radiation from
stoves, ETC., affect US as we'll as tn,
thermometer.
II the thermometer feels warm in tn,
sunshine, why not let it say so, as w
do ourselves?
Simply beause the effect of radiate,
heat on the therrn ometer gives no reli
able indication of it's effect on our
selves, nor are all thermometers, even
affected alike.
Two perfectly correct thermometer
which agree when ''slung" together il
, the shade, or when immersed in pal
of water, may differ greatly when hun
up in the sunshine. For the amount O
; solar heat absorbed by the instrument
varies with their size and shape, tn
quality and thickness of the glass an
, the character of the case. To say tina
the thermometer stands at 100 degree
. in the sun gives no valuable informs
, ton to anybody who does not know a
about your thermometer and the plac
where 1t hangs. The temperature c
the air is all that the house thermou
eter can be expected to indicate, and
, will not indicate this truly unless th
d. aforementioned precautions are taker
, Laurence b, Fletcher. M. D., in N.
= Ledger.