Year: 1874

Among the most interesting and important
practical results to be reached by the transit of
Venus observations is the perfection of the
nautical tables required for safe navigation.
While the splendid and costly equipments for
the various observing expeditions are being
lavished on science it is well that her enthu-
siastic votaries should take steps to secure the
highest utilitarian benefits derivable from their
labors. Few problems more deeply concern
mankind in general than that for determining
the exact position of ship at sea, and
errors, apparently insignificant in determin-
ing ships longitude lead to the most disas-
trous consequences.


In the practical solution of this last named
problem the moon and stars, when their
motions and positions are accurately ascer-
tanned, serve the purposes of the minute and
second hands of gigantic celestial clock.
The greatest nicely in ascertaining the time
requisite on the vessel at sea is obvious, when
we reflect that an error of half minute in
longitude puts the navigator four or five miles
away from the point at which he supposes
himself to be, and such an error is sufficient
to cast him on many dangerous coast. The
difficulty of approaching shore in security and
confidence has never yet been surmounted by
nautical science, and never will be until
means are devised for determining exactly the
true time. To show the value of such exact
ness it is only necessary to recur to a cele-
brated incident in the history of the Great
Eastern. On one occasion, when laying
the Atlantic cable, and when, of
course, in telegraphic communication with
Valentia, her captain wished to search
for buoy, which had been anchored at par
ticular spot known to him. He was then re-
ceiving By the cable be was paying out the
true Greenwich time to within second, and
gave directions for finding the buoy accord
ingly. At the calculated time when he ex-
pected to reach the spot sought for, and was
going on deck hoping to sight the object of
his search, the ships side was struck by the
buoy, showing how perfectly the true time
flashed to him from Valentia had rendered
his reckoning.


were absolutely correct the observer, by watch
ing the instant the moon comes to the posi-
ton of star, and knowing the exact Green
wich time at which she reaches that position,
receives an intimation of absolute time. Were
the tables of the moon, by which the mariner
computes his position, absolutely perfect Gas
they are in fact by no means perfect), he
could use the earth's swiftly revolving sat-
elite as huge chronometer, visible from
every part of the navigable oceans AS how
ever, the lunar motions are irregular. owing
to the enormous disturbing attraction Of the
sun, and as these irregularities cannot be fixed
till the suns distance is determined, the forth
coming transit observations are essential and
will be looked for eagerly by nautical philoso-
pliers.


Arrangements have been made for observing
the transit of Venus from about seventy-fvs
stations But although the great event occurs
on the 9th of December, 1874, it will probably
be late in 1875 before the grand result an
nouncing the suns distance can be reached
Many Of the observers will remain at their
respective stations for three m onths to perfect
their computations Of longitude. We may ex-
pect this large band of scientists to bring
home with them rich harvcsts of knowledge
from the varied scenes of their labors.