512 Curved Appearance of Comets’ Tails. (October, 
curve or a straight line, according as the observer is at one or 
another part of the earth, whereas a comet whose tail passes 
through the pole appears as a straight line or curve, ac- 
cording as the tail is directed towards the zenith or towards 
the east or west. Thus rotation in the last case produces 
the same effect as a different position of the observer pro- 
duces in the case of a comet on or near the equinoéctial. 
We need scarcely add that the same law holds good for 
nearly every part of the heavens. 
The reader who has carefully read the preceding remarks 
will be enabled to state exactly those conditions under which 
the tail of a comet will appear a straight line or@ curve. 
It must be borne in mind that the fact of a comet’s tail 
appeaying as a curve or arch to an observer on earth does 
not in the least prove that the tail of the comet is actually 
curved; it may be perfe¢tly straight, and will yet appear as 
a curve from the reasons assigned. 
There seems to have been some obscurity in the minds 
of former writers on. astronomy on this subject of the 
curves of comets’ tails, for we find the following statements 
relative to this curvature in the undermentioned works :—- 
‘The tails of comets, too, are often somewhat curved, 
bending in general towards the region which the comet has 
left, as if moving somewhat more slowly, or as if resisted in 
their course.”—From Herschel’s Outlines of Astronomy, Article 
‘‘The tails (of comets) appear to stream from that part 
of the nucleus which is furthest from the sun but seldom in 
the direction of a straight line joining the two bodies. They 
generally exhibit a sensible curvature.”’—IFvom Gallery of 
Nature, page 112. 
*““P. Bienewitz, better known as Apian of Ingoldstadt, 
concluded from what he ascertained in the instance of the 
comet of 1531, that the tails are always opposite to the sun 
and in the direction of a line joining the centres of the sun and 
the comet; but more exact observation shows that as comets 
approach their perihelion the tails are gradually bent more 
or less towards the region they have left, as if there were a 
resisting medium. ‘The tail of the comet of 1689 assumed 
the form of a Turkish scimitar; and that of the comet of 
1744 was bent like a quarter of a circle.’—From Smyth’s 
Celestial Cycle, vol. 1, page 221. 
*“ If no comet ever exhibited any other than this peculiar 
form of tail straight and directed from the sun, we might 
frame an hypothesis which could account for the facts; but 
in some instances there are many tails to the one nucleus, 
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