The L'Anse sentinel. (L'Anse, L.S., Mich.) 18??-current, 1899-07-01
Instruments Used by the u. s.
Bureau-Heat and
Humidity.
STUDY OF AIR CURRENTS.
Vanes Exposed to the Full We
lOcity Electrically Record Re-
suits on the Indicators.
From the New York Press.

From the New York Press.
All sorts of instruments and APP
paratus are used by the. United
States weather bureau to determine
meteorological conditions and pros
poets. For measuring the exact
temperature at its various stations
are the thermograph and the maxi
mum and minimum thermometers
The former gives II continuous rec
ord of the temperature; the latter
two show respectively the highest
and lowest for each "a hours.
For studying the pressure of the
atmosphere, the stations of the
weather bureau are equipped with
self-registering anerod paragraphs
and mercurial barometers. Read
ings from both are corrected for the
attitudes Of the station, and the
latter for variations In temperature.
The determination of humidity, or
relative humidity, as it is called by
the weather bureau, is accomplished
by means of two thermometers the
SO called dry bulb and the wet bulb.
The first is the ordinary thermom-
eter, by which the temperature is
indicated. The second is similar. eX-
cept that the mercury bulb is sur
rounded by cloth. which may be
saturated with water When this is
done, air is made artiticially to pass
over the saturated cloth, which
causes the water to cvaporate rapid
ly. The heat which is rendered
latent by this process comes from
the mercury of the thermometer,
making It descend. in the tube with
rlpidity proportional to that Of
evaporation. In dry air the latter
process is much more rapid than in
damp air, and by noting the differ
ence of the reading of the dry bulb
and wet-bulb instruments, and max
ing Il simple mathematical computa-
ton, the relative humidity is de-
termined. II is read in huhdredths,
100 meaning air saturated with
moisture, and zero air free from It,.
The former point is sometimes
reached, though never the latter.
The signal service makes use of
two instruments in studying the
wind-a vanc with automatic cleo
trical indicator for showing its di-
rection and the thermometer for
registering the velocity. Both ol
these are exposed to the unobstruct-
ed violence of the wind, though con
nccted electrically with the indicat
ors which are in the office below.
Both the instruments register con
tinually upon drum revoved by
clockwork, and at any time the di
rection and velocity of the wind car
be seen at a glance
The apparatus used by the weather
bureau for determining the character
of the day is known as the "sun
shine recorder" 1t consists of q
thermometer, with its bulb blackened
to increase the absorption of heat
from direct sunlight, inclosed in {
vacuum tube, TO prevent as far a.
possible the direct influence of the
temperature of the surrounding air
The piece of apparatus is in such a
position as to receive the suns rays
the entire day. When the direct
rays strike the blackened bulb the
mercury suddenly rises and closes
an electrical circuit, which causes Q
record to be made upon the revolv
ing drum in the Office below. Wher
the sun is obscured the mercury
drops again, and the circuit is
broken. The computation in tenths
Of the possible sunshine hours is
made by the weather official.
The latest device used by the
weather bureau for measuring the
! precipitation consists OF hopper OF
scale pan, which is constructed so as
to tip and empty itself, and at the
same time make an electrical indica
tion Of the fact in the Office below
for each !one-hundredth OF an inch
precipitation. BY counting these