The Indiana State sentinel. [volume] (Indianapolis) 1868-1895, 1874-07-21
SCIENCE BAFFLED.
THE LAST OF THE COMET.


COMET WHAT "oLD PRoBAB1LITIEs"
THINKS.
The New York Herald gives the summary
o the views of Gen. Myer, of t4e Signal
Service: IL is. however, with the tail rather
than the nucleus that we have now to do, in
so far indeed as it is possible to separate one
of these bodies from the other. The struc-
ture and chemical constitution of a comets
tail evidently depend directly upon the
chemical nature and physical con dition Of
the nucleus. Much has been said concern
ing the powerful effect of intense solar heat
upon such comets as approach near to that
body, and, indeed. these considera-
tions are in place in the of such
comets as that OF lS43, whose nucleus
approached to within 100000 or 100000 miles
of the suns center, and must, therefore, have
by but very little escaped grazing the sur
face of that tremendous orb, but in. the case
of the present comet, which, when nearest
the sun, is scarcely more distant than the
planet Venus, we evidently must have pres
ent peculiar conditions il the heat received
directly from the sun is To plav an impor-
tant pars in the formation of its tail. In ref
erence To this conspicuous appendage three
plausible hypothesis may b5 entertained
either that the nucleus may be gaseous
only, or may be an easily vaDOrized solid or
lqulu, WUOc6 NdpOT, UP uUO6f the
influence of solar heat, flows away as an
incandescent gas; or second the existence of
| a resisting medium in space may be invoked,
the friction between which and the nucleus
may give rise to the heat required for the
evaporation of the gaseous matter compos.
| ing the tail; or, third, the frequent impact OF
| of the myriads of metortes that are known
| to fill all space against the front of the comet
as il rushes along NAV suffice to produce the
| heat needed for the formation of its brilliant
/ tail. While there are reasons for believing
hat each of the three preceding suggestions
must, as occasion serves, be invoked as the
probable explanation of the origin of the
heat that is believed TO be necessary. on the
other band, in any case, it seems imppossi-
bic not to attribute very high degree OF
volatility to the solid or liquid matter form
| ing the nucleus. As rule
THE GROWTH OF THE TAIL
of comet takes place at the expense of the
nucleus. That of the great comet of 1911 had.
according to Sir William Herschel, a di-
| ameter of 42S miles at the period of its
greatest brilliancy, while Donati's comet,
in 1858 had diameter of 5000 miles in the
early part of its course, which subsequently
diminished to 400 miles. The comet at
present visible in the northern heavens be.
longs neither to the class of great Or of
| than 1000 miles in diameter. OF the chem
| ical nature of the nucleus and of its
vapor we can,n it would seem, no longer
| remain in doubt. The examination of the
| light of the tail of the two comets of 1868, by
means of the spectroscope, revealed to Mr..
| Higgins, first Of all, the possibility that its
substance consisted of gas intimately allied
| to defiant gas, if, indeed, not that very gas
itself; in fact, Mr.. Higgins stated that the
spectra of these comets agreed precisely with
| the spectrum of carbon, as obtained from
defiant gas, at least as exactly as it was
possible to conduct the observations. It is
\ customary in spectroscopic analyses to con-
slider so close coincidence as that observed
| by Mr. Higgins as satisfactory evidence of
the chemical nature of the body under ex-
| animation; but owing to the uncertainties
attending such novel Investigations
six years ago he announced his
| conclusions and alluded to the
difficulties that met him when he attempted
| to explain the origin of the heat necessary
| In order to render incandescent the come
tary matter observed by him through the
spectroscope. Since, however, Mr.. Hug
| gins observations have been repeated upon
| several succeeding comets, and we believe
| with invariably the same result, and since
| even the profound analyses of Mr.. Lockyer
have not yet suggested any definite, plausi.
| BILE explanation, we are probably justified in
| believing that the presence of certain three
| bright bands in the spectrum of a comet in
dictates that there is either mass of incan
| descent defiant gas, or else molecules of
| vapOr having q spectrum precisely like that,
and whose chemical properties may there
| fore be presumed to be similar. Those three
bands exist in Coggia's comet.
oLEFIANT GAS IN OUR ATMOSPHERE.
The question as to what phenomena would
probably be observed in case the earth en-
counters the tail of the comet may. there
fore, be answered by answering the ques-
| ton: What would be the consequence of
adding to the exterior earth's atmosphere a
layer of defiant gas having density faI
less than that of our present atmosphere at
the greatest heights to watch balloons have
assembled. Tyndall has shown that defiant
gas is one of the most powerful obsorbents
| of the heat rays. 1t follows, therefore, that
the mixture of possibly one per cent. of
/ this gas with our atmosphere would tend
| TO raise the average temperature of the
earth, since lis presence would hinder the
radiation into space of terrestrial heat, the
| total effect upon the mean annual tempera-
/ ture being az nearly as we can estimate less
| than quarter of degree Of Fahrenheit for
| stations at the Equator, and considerably
| less even than this for stations in our lati-
tude This dimunitiOn of terrestrial radia
| ton would have as a further consequence an
| increase in the quantity of moisture held
| suspended in the air, an increase in the Sc
verify of storms, and a still greater contrast
between the rainfall in the desert and in the
| weII-watered regions of the earth. But
considerations as to the possible effect of
adding to the earth's atmosphere a small
| portion of the comets tail seems altogether
| out of place when we consider that such adj
dition cannot happen unless our globe
comes into so close proximity to portion of
the tail as to
| DRAW IT TO ITSELF,
| and of this event there seems, in the present
case, but little, if any, probability. 1t has,
| indeed, been satisfactorily ascertained that
on two previous OCCASIONS during the past
century-namely, on June 80, 1861, and
November "a, 1S72-this very event did, in