New-York tribune., 1874-07-23
COMETS TAILS.

WHAT WE HAVE LEARNED ABOUT THEM.
THIS ONE WAS NOT HoLLOw-TTs DEVELOPMENT
ACCoRDANT WITH PFIRCES foRMULAs-lis
CURvATURE-THE REPULsIvE FORCE EXACTLY
EQUALS AND TAKES THE PLACE OF GRAVlrATloN
POSSIBLY THE TAIL WAS FLAT INSTEAD OF
CoNICAI-THE PARTICLES CONSTANTLY DRIVEN
AWAY FROM THE sun TILL LOST IN SPACE
TO the Editor OF The tribune.
SIR: The head of Coggia's comet has passed
nearly between us and the sun, together with the
brighter portion Of the tail. Whatever information they
would afford, from observation in the northern hem
fsphere already been obtained. The position OF the
orbit is known with certainty and accuracy What the
spectroscope has revealed will shortly be communicated
TO us For the last week the tail, stil visible In the
northwestern sky, has alone remained to give us fur
ther information. Now that that also is about taking
its departure expanding into huge proportions from us
proximity but fading into such dimness as almost to
Blbinets description or comet, "a Nsiple
nothing" let inquire whatwe have already learned
1t is evident that the tail Of the comet Is not ho"o"
for it's outline very dim. 1t is true that there Is
narrow central dark line; but even that cannot be
explained by the suns shadow falling upon particles
behind the nucleus by the nucleus interseptng
luminous particles repeed by the sun; for In either
case the dminution of the total light in the center
from the absence Of light for less than onetenth us
thickness. would not be easily perceived.
The discovery by Newton that the attraction Of the
earth. assumed TO diminish with the square OF the
distance would equal the cenrpetal force required 10
keep the in its orbit but small part OF the
demonstration of the law Of grdvitation. 1t was not
until 1t shown that all the peculiarties of the
motion OF the and planets were IN accord with She
theory OF gravitation that the demonstration was
complete. And when the law applied 10 explain
the motion OF comets the agreement of q comets
motion with that predicted upon his theory which
furnished the satisfactory evidence of ITS truth
The theory OF Prof Perce is; Each particle of the
matter which composes the tail is supposed to move in
byperbOc orbit the sun in the focus of the oppo-
site braLoh under the influence of a repulsiye force
emanatns the sun, and decreasing by the law OF
the inverse square Of the distance" Remarkable as
the accordance of the positions Of the front edge OF
the tail OF DOnats comet with this theory, there was
then ana has been since no opportunity until 10
apply the test OF prediction or Of the explanation OF
apparent anomalies, arising from the motion Of the tail
nearly toward US and from its proximity. At first the
tail of Coggils comet straight; afterward 1t
was seen bending forward in the direction OF the
comets motion; again 1t became straight, and finally
the curvature takes the opposite direction, here and in
the southern hemisphere. These changes, aud the close
agreement OF the position of the tail with the predic
tOns published in THE TRIBUNE before the comet was
fairy visible TO the naked eye demonstrate, first, that
the tail curved IN fact when appearing straight
and secondly it is bisected by the plane of the
comets orbit and they tend TO establish the theory
upon which the predictions were based.
works astronomy tell US that "the cOnveNity Of
the curve il exists is turned in the direction from
which the comet moves" it may be well 70 explain
here the curvature July l3 in the opposite
direction Referring to the diagram in THE TRIBUNE Of
July the earth being below looking upward at the tail
OF the it bends backward it is 10 curve to
the left while the comet to the right. The tail
seen July 49, TO to the left but the comet
did not appear toward the right, as Venus and
Mercury do when between and the because the
earth moved rapidly in right ascension than the
comet After passing the nodes the earth will be above
and them looking down upon the tail, 1t will appear to
curve the night. Although this anomaly, therefore,
apparent rather than real like the rerograde motion
OF the planets it illustrates the great difference Of
conditions between this comet and that OF DOnati,
strengthening the argument in favor Of theory
sistent with the motions of both.