The New Orleans daily Democrat. [volume] (New Orleans, La.) 1877-1880, 1880-01-07
SCIENCE OF THE WEATHER.
Something About the Signal Service
and its Apparatus.
Interesting Lecture by DIR. G.. III. Robe,
Signal Officer at this Port.

vol DIR. VI. IL hOne, SlEHhl 6iIiSfi ~ ta.S 49,"
Dr. Robe had chosen ms the subject OF his lee
ture the Science OF the Weather. and Tor
three-auarters OF an hour he enchalned the
attention Or his hearers. His delivery was
graceful and polished, and his explanations OIL
the methods of the signal service and the In
struments used were forcibe and clear.
His lecture was I'm substance as follows:
Metaorology treats of oil those more or less
perceptible phenomena which take place In
our atmosphere, and which we collectively
fern "weather." These phenomena are IA
military known and spoken OF as heat cold,
wind dew, rain, clouds, snow, hail, sieet, etc.
combination Of several OF them Is termed
storm, and IL Is the special business 81 the
nipnal service OF the United States army to
discover watch and follow up all storms,
whether large or small, destructive or other
wise, which occur wtthin the limits or pass
over any part OF the territory OF these ! ntted
States How this is acc ,mplished 1t shall be
my endeavor 10 explain 10 You IN as conpre
hensive and simple ~ manner "a possible.
In order to comprehend thoroughly ill
these conditions and phenomena n Will zoe
advisable TO briefly consider the elementary
principles VI meteorological science, and i
shall therefore devote the time at my disposal
this evening 60 a short account Ut such nrin-
eiples and the means by which they have
been discovered and formulated.
NItn Iris tHJHGh III NibW 4 Sllth UIbbtf9u W
define the meaning of The various expressions
In use La we lther lore, and describe tho
various Instruments by means Of watoh OBJ
Hervatiuns are made.
The atmosphere that envelopes the earth Is
n chemical mixture OF two simple gases, nj
trogen and oxygen, In the proportion of four
parts OF the former to one Of tho latter.
These proportions are tnvariable at oil times
and In oil places, notwithstanding the fact
that nitrogen Ia nearly twice as heavy as oxy-
in uvp rhx tppaI In yyA b,,tx
discovered by Daton--that gases are
equally dffused throughout their mass, with
out regard TO their different weights. This
law Ia technically known as the law Of dffu-
sion," or "Dalton's law" A small proper
ton OF carbonio acid and variable quantity
OF vapoI OF water is nearly always found In
atmospheric air, Upon the presence of this
latter component aqueous vapor depends to
q very large degree the various changes GO
Ing on In the atmosphere, which we term
weather.
The air, like oil gaseous bodies, possesses
Che quality OF expanding In all directions.
This quality Ia known rs expansive force OF
elasticity In virtue III this force the air
would be dispersed In cosmie space were 1t
not for the force of gravity which retains III
near the earth. As the force of gravity acts
much more powerfully near the surface OF the
earth than at a distance therefrom, tho accu-
mutation OF air Is much greater, In other
words, the air is deRscr Mt the surface OF the
earth than IL Is at u distance above Ii. This
greater density Of the air at the earth's sur
face Ia roughly shown In this diagram.
IL took science q long time to find out that
the air was body, and that u possessed
weight The natural science OF the aneients
was full OF verbal contradictions, and the air
was said to be light because 1t rose upward. |
while denser bodies were said to be heavy be- |
cause they fell downward to the earth |
Among the discoveries or the famous Calico
was that OF the weight Of the atmosphere,
while Torficelli, pupil OF his, invented III
the barometer, means Of measuring the
amount OF this weight. or, as 1t iS technically |
termed, It's pressure.
The ordinary lift-pumps had long ago
taught people that water could be
made to rise TO a considerable height by re- |
moving the air from above It, This phenom-
enon was explained by the science of the day |
by saying that mature ahhors a vacuum" |
IL was known. however, that this "abhor-
renee" Of nature only held good within GER
lain limits and that the vacuum was not filled |
by the pursuing water If the piston was
raised more than thirty-three or thirty-faur
feet. Torricelll reasoned correctly that such |
y Limitation should not occur II the explana-
lion was a true one, and, as q result oil his
thought and experiment, we have the barom-
eter, which means weight measure.
In the barometer the air Is weighed and
This weight Ia announced to the observer In
plain figures-not In pounds aud ounces, but
n 80 many inches of mercury; that IS, as the
weight OF a column of mercury a quarter of
M inch In diameter and thirty inches high
balances u column OF air Of the same diame-
;er, and reaching from the surface of mer-
surv In the cistern of the barometer to the
Jop of the atmospheric envelope the weight
DE- pressure OF the atmosphere is said to be
,uuai to thirty inches OF mercury, which ia
Ito average normal pressure at the level Of
the sea. AS we ascend above the sea level the
in the barometrie tube deecends, or.
ss we cay. the barometer falls. This falling
II the mercury In the barometer Is due, as
Will be readily seen, to the removal OF weight
n pressure corresponding to the ascent.
For example: At 1856 n. M. Washington
mean time) of April 2s 1878, the barometer at
San Francisco. Gal, before being corrected
or elevation above sea level, read 30 - inches
lt the same time the instruments at Denver
md Pixies Peak, Col. read 24S2 and II &C. re-
pectively. You will see, then, at once that
he difference OF pressure between the eleva-
Ion above the ocean Mt San Francisco aud at
Denver and Pixies Peak, amounting In the
ormer to .53l inches and In the latter
o 12H inches, measures the weight
Il that air which Is below Pixies
Peak and Denver, and above San Francisco
1t the latter station this air exercises it's
PRESSURE upon the barometer, and this nstru- |
nent reads 3013. At Pixies Peak a vertical
olumn Of air Of nearly three miles In height
q below the barometer, and, consequently,
an exercise no pressure upon IL. The weight
II this intermediate column of afr IL hence.
g shown by the readings, equal to a column {
y AheASWy iAtt lHGutS ulRH. LII VIII LluS De
lear to every one that In order 10 be enabled
% compare the readings Of the harometers Mt
he stations named they must first be re- I
Iuced to common level which Is the mean
'cean level.
Knowing the elevation Of these three sta
IONS above this ttXrtt level. anti applying tic
we find that on the twenty-eighth
u April, 1878, at 80 a. m. Washington time)
he barometers at San Francisco Denver
md the summit OF Pixies Pike read respec-
lively 1920, 5000 and 299s. Thus while, be-
one correcting for elevation, the difference tn
pressure between San Francisco and Pixies
Peak was 12,47 inches, after making the
correction. the difference of the readings
vas az inch. This latter was the actusl diff
erence In pre- ssure under like Typographical
conditions, and was due to differences in dem
lily or quantity OF vapor present.
The earth and the atmosphere that sur
sounds It receive their heat from the sun.
The air is partly heated by direct absorption
rom the suns rays, as these pass through {
he atmospheric envelope, but the larger ]
lmount of the heat of the surrounding air ia
derived from the earth by radiation. It Is a
act, which has been demonstrated by Tyn-
Ahn& al. Ire ~, l