New-York tribune., 1874-07-04
COGGIA'S COMET.

PREDICTIONS FOR THE NEXT FORTNIGHT.
COURSE OF TUE COMET SINCE ITS DISCOVERY
METHOD OF CALCULATING ITS oRBIT-PosITIoN
AND BRIGHTNESS TO JULY 20-A CASE WHERE
THE EARTH PASSED THROUGH COMETS HEAD
THE PARTICLES OF THE TAIL WHICH MAY REACH
US START FROM THE COMET TO-DAY.
70 The Editor OF The Trfoune.
SIR A new comet visits us every few months.
transit of Venus occurred for more than CEN
tury II s not surprising, therefore. that when the
principal astronomers in the United States were pre-
pairing depart Transit expeditions, leaving at home
only those Who could be spared from other duties
not one OF them should have remained to receive
the visitor announced from the celestial spaces,
and that the entertainment Of an angel una
wares should have been left to those comparatively
unknown in the scientific world The observatOries have
spoken they have had too much routine work which
could be neglected for apparently useless computa-
ons and that the time has arrvedfo for their action,
they will much to do in making and reducing
their observations that II is hardly 10 be expected that
we shall soon hear from them. In the mean time the
public mind has become huge interrogation point; and
the prospect ia that il have reasonable
amount OF clear sky, 1t will be difficult for the next
three weeks 1.-THE OF the questions that will
be asked about the comet With your kind permission
will at once lay before the readers Of THE TRIBUNE
the means Of answering some Of those questions.
EARIY ANNOUNCEMENTS OF THE COMET
On the nth OF April NJ. COggia at Marseilles, dis
comet, too faint TO excite any particular
attention IL the third comet discovered during the
present year. and although believe both the others were
announced by cable did not any announcement Of
this From the observations of the first five days an
orbit was computed which published in the AstrOnO
rntSehe Naehrhten for May from which IT appeared
that the comet would move rapidly southwark and be
lost the suns rays before the end OF june developing
f1 brightness SO times that at the time OF discovery
Early in June 1 received Nature, dated May q, which
fnad
the orbit computed by Dune in the AstonOmische Mach
ytehtn for May 49, derived from observations up 10 May
g. from which appeared that the comet had changed
Its mind aud concluded 10 go south until the sd Of
August when It TO be 2i5 tunes as bright as when
first discovered. / Immediately decided TO look It up
but before clear evening presented ITSELF Lewis Swift
OF Rochester whose name had been associated with
comets certainly early 1885, in sweeping the heav
ems discovered what he supposed to be new comet;
aud # was announced by telegraph in The TRIBUNE and
other papers the following day On the l?th found
It, and determined its position by reference to Ar
geanders charts and the Bonn Catalogue and that
it was not moving accordance with either of the
puted orbits; that all the conclusions drawn from
them we're erroneous computed another orbit, my
conclusions from which published in THE TRIBUNE
OF June 23
DATA FOR COMPUTING THE ORBIT
"But how do you know is not equally IN error
Let me explain 1t by an illustration. Take your stand
ball Almost as soon 1t strikes the boards you
see whether or not it will 90 entirely wide OF the mark
but 1t until 1t approaches quite near the pins that
you can determine with precision where 1t viii strike
Astronomers have moro accurate means Of determna-
ton but the other hand, they have TO deal with
bodies at immense distances, and moving In curved
paths Another illustration: Draw circle six or
eight inches In diameter and prick through the paper
three points upon the circle inch apart into another
paper. Then, you attempt to ascertain from those
pin holes the size OF the circle its path at distance
OF six inches from the pn-hoes, you will fnd your
suits grossly Inaccurate Replace the original paper,
and prick through another point inch away and now
st becomes easy determine the circle much
rectly Replace again. and prick through points
two three inches further away; aud you de-
termine the entire circle only with great accuracy
but with absolute certainty. Tue first orbit from
observations comprised within five days; the second
within less than three weeks my own from observa-
tions extending two months 50 far, therefore,
shall give statistics with reference the position or
motion Of the nucleus Of the comet the naccuracy will
consist wholly in my giving round numbers and not iu
the use Of an inaccurate orbit.
POSITIONS RELATIVE TO THE EARTH AND sUS.
BRIGHTNESS, &C.
According to the latest determinations tho orbit q,
the comet inclined TO the ecpc at angle OF CO.
and TO the equator at angle OF SO Its nearest ap
proach 10 the is at distance very nearly twothiras
OF that Of the earth. aud little less (onefourteenth
iess) than that OF Venus, and will July The
general facts Of the distance OF the from SUM-
its distance from the earth, and its briGhness, com
puted upon the usual theory may conveniently
compared II put in tabular form. shall assume the
earth distance from the sun to be 100000 miles
oeorrespOnd with the later determinations or the suns
paralax. and which is probably much more accurate
than the distance OF s5,oOoOOo, TO which we for
mery accustomed