Public ledger. [volume] (Memphis, Tenn.) 1865-1893, 1874-07-16
The PerfheIfOned COmet-Its Posi-
BILE InterpIaneIary Influence.

The arrival of the comet at its perihe-
lion on the Sth inst, give a new turn to
its history, which will be steadfastly
watched by its many admirers. The
great meteor is now about one third
nearer the sun than we are, or about
sixty millions of miles from that fiery
orb. The effect Of this approach to the
sun is necessarily great in the analysis
OF the cometic matter by solar heat and
the yaporization of the meteor.
The only explanation that has been
gwen Tor the apparent contraction Of
comets as they are perihelioned is that
they are partly evaporated by the heat
and the cosmical cloud is converted into
invisible cometary mist The whole mass
OF Halleys comet, in 1856, was thus
conversed into invisible gas, and after
wards, on cooling, was condensed so as
to become again apparent. The change
which the great comets undergo from
their near advance toward the sun is one
of the most interesting points of investi-
cation in terrestrial physics for, from
what we know of the powerful agency of
aqueous vapor on our planet, we may
not unphilosophically conclude that the
cometary vapor, expanding over millions
of miles in space, plays for the time being
an important part in the distribution Of
solar heat through the solar system.
Every one has observed on an intense
ly hot midsummer day what boon a
small feecy cloud flying overhead is to
the pedestrian in screening him from the
rays above. If condensed, such cloud
would probably not furnish water enough
to moisten a handkerchief, but the va
porous particles are potential in arrest
ing the down-pouring flood of solar radia-
ton. We know that the water Of the
tropical ocean, when converted into in
visible vapor, occupies between sixteen
and seventeen hundred times its original
volume. This is, however, only under
an equatorial temperature of from eighty
FIVE to ninety-fye degrees Fahrenheit
very low temperature, comparatively.
But in the vaporization Of comets, when
at the perihelion. a temperature ranging
from FIVE thousand TO twenty-five thous-
aRd times that of an equatorial sun, is
brought to bear upon the cometary mat
ter
The inconceivable attenuation and ex-
pansion due to such thermometric ex-
tremes can he family indicated only by
immense cometary clouds. stretching
over many millions of miles in interplan-
etary space, and serving to divert or re-
tard OF stop the tides of solar heat. 1t
would, therefore, not appear remarkable
should accurate research hereafter prove
that comets have an important influence
on the climate and weather Of the season.
Such has been the world belief for ages,
and though modern science, with its
iconoclastic tendencies to sweep away
all that is old may reject the thought
maturer results may confirm it.
Should the perihelioned comet of 1874
exert this influence, as some think it has
done already, the effect will be most
marked perhaps, in reducing the July
thermometric mean The cometof Cog
gia will, now that it has made its closest
approach to the sun, rapidly pay its re-
spects to us. According to the reliable
computation of Astronomer Hind, the
great meteor will be nearest the earth on
the night of July p 1t will then be less
than one.third of our distance from the
sun, or within thirty millions of miles of
our globe.