New-York tribune., 1876-10-13
TRIBUNE WEATHER DISSERTATIONS

TRIBUNE WEATHER. OboEhf dIiOND'
Our readers have for some time past become
familiarized with TIE TRIBUNE's diagram OF
the barOmetrc curve, accompanied by Drlel
observations on the weather and forecast OF
its probabilities. The occasion for this under
taking may here be briefly stated. The TRIB-
UNE has never hesitated to cOncede hearty
admiration of the work done by the U. 5.
Signal Service. Its system of procuring re-
ports is thoroughly organized, and its trained
corps of Observers-many Of them at lonely
and distant pOsts-periOrm their laD0rs Win a
fidelity that is rare in Government employ.
Their reports are digcstcd at Washington by
an expert peculiarly qualified for the business;
n gentleman who has made the science OF
meteorology profound study; who brings to
bear upon the daily predictions of the weather
all the knowledge which recent advances in
that science can supply. Hence those predic-
tiOns have become marvel of accuracy, ana
have elected unqualified praise from those who
are competent To judge of their merits, abroad
os well as at home. But the Government
weather reports are framed to cover broad
regions. They rarely or never specify the
weather of particular localities. They are
cancellations. And they scrupulously
avoid prediction for more than twcnty-fOur
hours III advance. 1t needs not to
be demonstrated that such "prObabil-
itics" must more or less fail in describing
the weather of separate places. Let anybody
who has spent a Summer month. for instance,
at Trenton Falls in this State or among the
mountains of Pennsylvania, compare his ex-
perlence of weather dag by day with that OF
his friends who have stayed in this city, and
he will find wide discrepancies. Yet these To-
calitics would come under a single description
of weather in the daily predictions of the Gov
ernment TIE TRIBUNE has perceived the need
of a local weather report for New-IOrk City
and vicinity; not as superseding but as supple
menting the Government predictions. A fur
thcr effort has also been made to give notice
of coming storms for more than twenty-fOur
hours ahead, when they are of probable i'm
portance.
These observations were begun as an eXper-
iment. No claim has been put forth respect
ing their accuracy of prediction, since tins Is
a matter in which our readers can judge for
themselves. The chances of error increase in
geomctrical proportion with additions to the
time ahead for which predictions are made;
hence those that attempt two or three days
instead of one are far more likely to be mis-
taken. But while it is quite safe to set down
any man as Il charlatan who in the present
state of meteorological science should attempt
to predict the weather for Il month ahead some
notion of what is probable for at least two OF
three DAYS 10 come can usually he given with
ont the risk of hagrant error. A brief resume of
recent results will show how far THE TRIB-
rNE predictions have proved satisfactory. For
convenience we take the period Sept. to Oct.
10. thiriy-six days of much varied weather.
In that time each of the half-dozen larger
storms was correctly predicted, and nearly
every one i8 hours in advance The rate OF
their approach or the time when rainfall ac-
tually began has in two or three instances
varied Il few hours from the calculation,
tbougb never as much as half day.
Although no storm of magnitude was missed,
there is one instance where light intermittent
rains, lasting during morning, were not pre-
dlcted: in only one ease where heavy storm
was forctold did failure enSue, and then the
disturbance passed to the north OF us, leav-
ing Ncw-YOrk City untouched by ram. There
are occasional instances where the amount
of cloudinrss was inaccurately estimated, or
where prediction of change of temperature
or way of the wind was not strictly verified.
But there are no grave mistakes III TINS peil0d,
and i'm more than two cases Out OF three the
authorizations have been justified i'll every par
ticular
Chief among the means by which these
gratifying results have been attained. is the
instrument named by it's inventor Prof. H. y.
Clum of Elmira, n. " the aGllograph. This
il an automatic recording instrument, and the
curves in the daily diagrams Of The TRIBUNE
arS an accurate transcript of the pencllings
furnished by the changes in the weight of the
yicwless air. Aside from Its capacity for self
recording, the instrument Is tar more sensitive
to atmospheric changes than the ordinary
barometer This is due to its peculiar con
struction float rests on the surface OF the
column of mercury To this float rods are
attached which descend through the mercury,
beneath the lower edge of the tube, ana turn
up on the outside of the tube, passing through
the cstem of mercury in which the tube
stands. The upturned ends of these rods
support several large air-tight cylinders;
the whole weight thus carried by the
float exceeding twenty pounds. As the
air which these cylinders inclose is of
an unchaneing weight, while the atmosphere
outside is constantly varying in density, they
assist materially in giving to the instrument a
ouick scnsitlveneSS to changes of pressure.
Allowance has to be made with ordinary
barometers for the fact that changes of tenn
perature raise the mercury to different nights.
In the aCllograph this discrepancy is entirely
avoided; the record being that of the hight OF
the float. The float sinks little deeper in the
rn.rcurV when thp lottpr il ovnonded nv