The herald., 1895-02-21
Where Thermometers Should
Be Placed
EXPERT FRANKLIN'S VIEWS
Interesting Facts About Currents of Hot
and Cool Air
An Approximate Temperature Of Large
nass of Air the Object Of the
Weather Bureau

In Southern California the question o
weather is essentially a business one.
There can be no doubt about this when
a drop of a couple of degrees in the ther-
mometer may cost this section several
millions of dollars, if it happens at a certain
time. Hence the question of temperature
is a most important one and is given
much attention by good many amateur
observers, as well as by the official Gov
eminent expert, who is stationed here.
For years past there has been consider
able amount of friction between the out
side observers and some of the general
public on the one hand and the local
Weather Bureau on the other, the ques-
ton always turning on the records OF
low temperature and the location of ther-
mometes. That of the Weather Bureau
is located on the roof of a high building
on Spring street in the center of the city,
while those of most of the amateur OBJ
servers are placed nearer the ground. 1t
is naturally to be supposd that the Gov
eminent department, which makes a spe-
cialty of keeping track of the weather,
should know what it is about and adopt
methods which experience has shown to
be the best. At the request of The Her
aid Mr.. Franklin, the local weather OBJ
server, has furnished the following re-
marks on the subject of the location of
| thermometers:
THAT feature of thermometer exposure
which most affects the extremes of temp
erature, as recorded by the Weather Bu-
reau, is the altitude of the thermometer
shelter, and that, too not only above the
roof of the building and above the
| ground at its base but especially in its
! relation to the topography of the ground
| for several miles around the station. As
| the Weather Bureau thermometers are
established at an elevation OF 10 to 10 feet
above the roofs OF high buildings or, fail
ing these. 10 feet above some elevated
| ground and are, therefore, exposed to any
| breeze that may blow, therefore the max
| ina or midday temperatures are not often
SO largely affected by the height above
the ground as are the minima or
especially during calm nights, the cold
air settles in the low lands and flows down
rivers, valleys and ravineS as far as fresh,
cool air can be supplied from above.
Thermometers stationed on high build
ings are often entirely above the layer of
cold air near the ground beneath them,
and similarly with the thermometer in
| low valleys, as compared with those on
bluffs and hills near by. Consequently
| minimum temperatures, as reported by
regular Weather Bureau stations which
i are elevated as much as possible above the
| surrouding region, are appreciably higher
than those reported from voluntary sta
tions in the neighbohood, since the latter
/ are almost invariably near the ground
No correction has been made for this
| source of discrepancy. The very object
| of exposure at such attitudes above the
| taI b,- ha tbar
Bureau, is to obtain an approximation to
! the average temperature OF a large mass
| of air flowing by the station and forming an
integral part of the circulation around
areas of high and low pressure. The
temperatures thus observed are espe-
cially adapted to the needs of dynamic
meteorology, whereas those observed by
| thermometers nearer the earth's surface
are appropriate to the study of climate in
| its relations to animal and vegetable life
| within very restricted areas.
William NJ. Davis, professor of physi-
| cal geography in Harvard College, speak
| ing of nocturnal temperatures in his re-
cent treatise on meteorology, says that a
| general decrease of temperature is en-
countered as we ascend the atmosphere,
! but in the case of the air over dry pla-
! teau on long winter night, the cooling
| OF the lower layers may be so great as to
reduce them to de cidedly lower temp
erature than that of the air at the height
of several hundred feet aloft.
| "Such condition is known as an in
version of temperature. This condition
NAV prevail about sunset, the tempera-
ture OF the air then being between the
! extremes of high noon and late night.
When the suns rays are no longer felt
the cooling that had begun in the after
noon is continued for time more rapidly,
and the whole mass of the atmosphere is
somewhat reduced in temperature. At
thn 1n1a SIirfan ,f fha
cools much more rapidly. and by midnight
it may have fallen to temperature close
to Fahrenheit zero. The air near it is also
greatly cooled by radiation and conduc-
tion to its cold surface, and before morn
ing falls to temperature much lower
than that of the air many feet above the
ground. The decrease of temperature by
radiation from the ground progresses
rapidly at first, when it is but little cooler
than the air above it; but late at night,
when Il strong contrast of temperature
between ground and air is developed
further cooling of the ground and thus of
the air close to it, is somewhat checked
by radiation from the above. As the
lower air cools, its expansive force de-
creases; the everything air, no longer borne
up by expansive force equal to its weight,
settles down a small distance, COMPRISING
the air beneath and thus increasing its
density and restoring its expansive force
to its former equality with the weight
from above.
''rhls process is not intermittent in ma
ture, but is continually operating at every
level in the atmosphere to maintain the
equality between the downward weight
from above and the upward expansive
force from below diversions of tempera-
ture are of much commoner occurrence than
is generally understood. They probably
occur to greater or less degree every
clear night on our dry Western plains!
EXAMPLES of their effect, NAV he often seap
in small way in late spring frosts, when
lower leaves of shrub may be nipped,
while the upper branches are unharmed.
In larger way and aided by other pro-
cesses the milder temperature of low hills
than that of adjacent valley bottoms at
night could be explained, and it could
also be shown that the quietness of the air
at night depends largely on the occurrence
of or approach to temperature diversions
of the kind thus explained
The Bank Robber Held
.,.+L bo