Lincoln telegraph. [volume] (Bath, Me.) 1836-1846, 1841-10-07
LINCOLN TELEGRAPH.
Bath, hlr.
THURSDAY MORNING, OCT. 2, 1s41.
Prof. Espy---His Theory.


tended and excited general interest; and so lar
as we learn gave entire satisfaction
In relation to the various positions discussed
and SO ably fortified, in the course of these Lee
lures, we cannot from cursory hearing, be
presumed to understand them all with sufficient
accuracy, to present any thing like correct and
general synopsis. He commenced by stating,
that the wind blows Inwards on all sides of
storm towards its central parts towards point,
if the storm is round, and towards line, If the
storm is oblong-extendlng through It's longest
diameter This position was amply sustained by
evidence gathered from the examination ofsome-
thing like twenty storms, both by simultaneous
observations in their centres and all round their
borders. In all his examinations upon this point,
he had not yet found one exception to the posi-
ton. The philosophy of these facts he accounts
for thus
"When the air near the surface of the earth
becomes more heated or more highly charged
with aqueous vapor, which is only ive-eighths OF
the specific gravity of atmospheric air, its equi-
librium is unstable, and up-movng columns or
streams will be formed. As these columns rise,
their upper parts will come under less pressure,
and the air will therefore expand as it expands,
it will grow colder about one degree and quar-
ter for every hundred yards of its ascent, as is
demonstrated by experiments on the nePhele-
scope IAN instrument of his own invention for
that purpose). The ascending columns will car
ry up with them the aqueous vapor which they
contain and, if they rise high enough, the cold
produced by expansion from diminished pressure
will condense some of this vapor into cloud; Tor
it is known that cloud is formed in the receiver
of an air pump when the air is suddenly with
drawn The dist ance or height to which the air
will have to ascend before it will become cold en-
ough to begin to form cloud, is variable quant-
ty, depending on the number Of degrees which
the dew point is below the temperature Of the air
and this height may be known at any time by OBJ
serving how many degrees a tim metallic tumber
of water must be cooled down below the temper
allure of the air before the vapor begins to con-
dense on the outside. The highest temperature
at which it will condense, which is variable ac-
cordinr as there is more or less vapor IN the
air, is called the dew point and the difference
between the dew point and the temperature OF
the air in degrees is called the complement OF the
dew point.
1t is manifest, that if the air at the surface OF
the earth should at any time be cooled down a
little below the dew point, 1t would form log
by condensing IL small portion OF Its transparent
vapor INTO little fine PARTICLES OF water, and II 1t
should be cooled twenty degrees below the dew
point, it would condense about one hail It's Vapor
into water, and at forty degrees below, 1t would
condense about three-iourths Of Its vapor mic wa
ter, &c This, however, will not be exactly the
case from the cold produced by expansion III tile
up-moying columns; Tor the vapor Itself grows
thinner, and the dew point tails about one quarter
of degree for every hundred yards OF ascent
1t follows, then, as the temperature OF the air
sinks about one degree and a quarter Tor every
hundred yards Of ascent, and the dew point sinks
about quarter OF degree, that as soon as the
column RISES as many hundred yards as the com
plement of the dew point contains degrees OF Fab
renheit, cloud viii begin TO form; or, in other
words, the bases of all clouds forming by the cold
of diminished pressure from up-movng columns
ofair, will be about as many hundred yards high
as the dew point in degrees is below the temper
ature of the air at the time. If the temperature
of the ascending column should be ten degrees
above that of the air through which passes, and
should rise to the height of 800 feet before 1t
begins to form cloud, the whole column would
then be L 90 feet of air lighter than surrounding
columns and if the column should be very mar
row, its velocity of upward motion would follow
the laws of spouting fluids which would be eight
times the square root Of 100 feet second, that is,
so feet a second, and the barometer in the centre
of the column at its base would fall about the
ninth of an inch. As soon as cloud begins to
form, the caloric of elasticity of the Vapor or
steam IS given out into the air in contact with
the little particles of water formed by the CON
densation of the vapor. This will prevent the
air, in its farther progress upwards, from cooling
go fast as it did up to that point; and, from ex-
perments on the nephelescope, it is found TO
cool only about one half as much above the base
of the cloud as below that rs, about five eigths
of degree for one hundred yards Of ascent, when
the dew point is about seventy degrees If the
dew point is higher, it cools little less, and if
the dew point is lower, it cools little more than
fve-eighths of degree in ascending one humid
red yards.
When up-moving currents are formed by supe-
rior heat, clouds will more frequently begin to
form in the morning, increase in number as the
heat increases, and cease altogether in the eve