The New Orleans daily Democrat. [volume] (New Orleans, La.) 1877-1880, 1880-01-21
WEATHER WISE.
Something About the Wind System
and the Laws of Storms.
Hecond Lecture or DR.. q. III. Robe at
the Academy of Sciences.

The announcement Of the second Of the series
~ Iaeturaz On the Science Or the Weather hy
DR. Geo. II. Robe, signal officer at this port. lss'
uiaht attracted to the Academy Of scienoes .
large and Intelligent audience. DIR. Rohe had
ni,t,zs.tt ~ he -, hiant If his Discourse.
rHr WIND srsTRa AND THE LAVE o. STORMS.
and HE address was both entertaining and
instructive. In opening he hnatily reviewed
the points Of bis previous lecture. and then con
tinued AZ follows
the ar he exee. eively heated II expands and
risea ita place being rapidly occupied BY the
colder air which r iva In from the surrounding
regions. ii the heating Of thiH central area
continues, the inn WING air aRn espandH and
ascends and the process may continue ,hae en-
ney The hnr,ons centric , meta9n 81 .na
air ahsorha additional ~. tatura--siuce, ns we
have Heen the capacity Of the air for absorbing
nos,nre e Ell wa 5ha have
thus two forcea heat and moisture. acting In
concert to produce diminution OF density,
and consequently, decrease IN pressure;
Thua II will he nj once understood that local
Increase oF Temperature or Of moisture or both,
occasion mt only an upward current q air, hut
alao n horizontal current or wind. The arat
eayae of wind Ia. therefore, local Increase 81
Temperature knowina. then. that the oocur
renee Of wind preanpposes the eSistence q diI-
al airlthja difference of pressure depending I'm
the frat place upon difr srenees of tenn peratura
we may proceed to formulate our first law,
which In this.
Wind IL the result Of differences OF pressure
Temperature and humidity of the air. The
toward n region Of low barometer: from re-
Eion OF low tmperaiuIe toward . region Of
high temperature, and from region OF com
pRrativelY dry OR toward . region 81 humid
Hence, II northerly wind ia blowing at New
Orleana. we would. assume that the pressure ~
n rutt mad mil tfv
lower % the north Of US. cay over the States 81
MiseIseippi and Tennessee than to the aouth.
we would assume these conditions to be re-
Having stated our law, and Illustrated II BY
saampe We can now pnGcee e,re TO sIhap nn eye s
globe. wi h q reasonable hope TINT WE shall be
able TO give y cause for each of the phenomena
The statement was made. In form OF general
proposition. that the normal pressure Of the
atmosphere at the level Of the sea IL thirty
inches. This II not entirely correct. II ia
found, In fact. that some regiona Of the earth
show an hsh,tualiY higher. while others show
an hahi,uallv lower pressure. remembering
then, our flret law wa will at once conclude that
the wind hlowa continually from these regions
pt higher toward the regions OF lower pressure.
The Hun's rays, reaching the surface Of the
globe vertically a. the e1uaor, produce In con;
sequence Of their h.a Ing, power. an upward
tensiiied By the evaporation. Of enormous guam
titles OF water, which ascend likewise. az yapor.
The air which haa thus aasended must be re-
placed 10 reetore tho equilibrium. and the air
from the surrounding region ruHhes IN 10 90
cupy the partial vacuum. But this air alao
comes under the heating influence. and becom-
ing rarifled In It's turn also ascende To give
place to u atll further Increment, aud thus tho
process continues indefinitely. This horizontal
air current is part Ct great s sgstem o. atmoa
This constantly ascending current. carrying
with Il immense quantities Of aqueous yapor,
s soon te .s an elevation where large nor.
cold uf these higher regions. Tbis forms dense
mssses of cloud, and Ia preeiptated In the
fern of copinus showers of rain. Indeed SO
constant IL this cloudnesa at the equator that
the sal ora term II the cloud ring Wind
ctorme are almost unknown In this region.
tent and duration. Thunder atorms and vio-
lent rains are, however, OF daily occurrence In
this equatorial belt Or zone Of oalms. aud fire.
auently furnish vessels with needed Supplies
q fresh water. i s In this calm. belt that Thee
hs her1 with his M and child to
hulk. until nnaliy. BY lucky chance, or the
neceet itttE OF the atory.R landWard current
carries them ash re on n tropical sand.
The progressive condemnation Of the uprising
current finally checks its ascent and the air
nows Of latafally. or ating Q current which
takes direction opposite to that ~ tho surface
This counter current was named by Maury the
''antl-trsde" ThtH anti trade blows from tho
the tropics Il a. ain descsnds toward the earth |
and portion OF II Joining the surface CUR ent
toward The eannstor asain forms part Of the
trade wind. The remaining portion Of the
anti-trRde gradually deacepds to the surface OF
the ear h AM Continues Its way toward the pole.
tormine the su, face current Of the middle iati-'
tudes.
Where the counter trade descends ID. The
earth. namely. In the latitude of the tfbpfrs. |
there t. also bsI q Gains or variAhlg s
This tropical calm belt L. however, o region of |
hfGh pressure. while the equatorial palft brit ID |
one Of low PRESSURE Hence The trade Winds |
blow from the tropics I'm the northern and |
southern hemisphere toward the eduator. TIL
difference Of pressure between the Tronlc OF
Cancer and the equator Ia 2ss inch the average
while al the tropic 1t is 80 40 inches. This DIFF
ference of pressure will nj once furnish the
reason for this constant current. which is 50
valuable for the pursuit OF commerce
To avoid any unnecessary complication Of
the subject, have hitherto assumed that the
trades blow In . straight north and south d.
&C rest such would undoubtedly be the case
But ne You we'll know. the earth makes COM
plete revolution on Its axis once In every TWEEN
winds different direction and Instead or the
north and south wind. we have q northeast and
ment and understand how this change OF dree-
ion Ia produced.
The earth revolves upon is axis from west to
east. com pleting the revolution once In TWEEN
Ey-four hours, The diameter Of the earth be-
Ing greatest. however. at the equator and d.
toward the poles. It is manifest that
The surface at the equator travels through a
greater space In the same time than II does In
he higher latttu les. The velocity eastward at
he equator is 1886 miles per hour while In lati-
tude 80 degrees 1t ia saT miles per hour The
atmosphere, being In contact with the surface.
moves at the same rate. IT, then q mass of air
we're suddenly transported from the equator to
latitude 80 degrees 1t would travel eastward AT
he rate OF 1879 miles per hour faster than the
sarth, and would manifest itself a. hurricane
rom the west with that velocity. If. on the
contrary. a mass Of air were transported from
he psrailel of 80 degrees to the equator II
would lag behind a. the rate of lSa miles per
hour. and would; hence, exist rs storm winl
rom the east OF that velocity. The friction be-
ween the afr and the earth would gradually
equalfye the motion of the two, and the condi-
don of equilibrium be established,
or course. It Is not TO be supposed that such
IN extreme case of sudden transportation ever
occurs. But you will understand that body
u air starring from the latitude Of the Tropte OF
Cancer and travelling towards the equator, IL
,ontnaally losing time and tagging behind the
'@rfhs Instead OF moving directly south 1t
ends 20 assume a westerly direction and what
began as northerly wind becomes gradually q
wind. This we know as the
The commencement at the