510 Curved Appearance of Comets’ Tails. [O&tober, 
horizon, HP RSZ a portion of the equinoctial, and PRS 
three stars on the equinoctial. The line P RS will appear 
as a curve or arch. 
We will now suppose that s is the head or nucleus of a 
comet, and that the tail extends along the equinoctial and 
as faras Pp. The comet’s tail would now reach from P to 
R and s, and would appear as a curved line or arch to an 
observer in 51° latitude and to observers in all middle 
latitudes, but as a straight line to an observer at the equator, 
or to one at the North Pole. Consequently the curving or 
bending of a comet’s tail is in this case an appearance only, 
due to the position of the observer, and the same comet’s 
tail may appear at the same instant to two observers, one 
in middle latitudes and the other at the equator, as a curve 
and a straight line. 
When the comet’s tail is extended in that part of the 
heavens near the North Pole, a quarter rotation of the earth 
will produce similar effects to the preceding. Asan example, 
suppose the head of a comet west of the pole and the tail 
coincident with the great circle passing from the west point 
on the horizon through the pole, then the tail being 
coincident with this great circle would appear curved. 
In six hours the comet would be on the meridian and 
below the pole, and the tail being coincident with this 
meridian, would now appear as a straight line, whereas 
before it appeared as a curve. ‘Thus the curvature of a 
comet’s tail is an appearance only, and is due to the same 
law as that which causes the pointers to sometimes appear 
to point more dire€tly towards the pole star than they do at 
other times. 
During the year 1861 we happened to be staying in 
Hampshire with a friend who was a close observer of 
Nature. We were walking in a wood a few minutes before 
sunset, when happening to look at the sky through an 
opening in the trees, we remarked a bright object larger 
than Venus at her greatest brilliancy. The object we at 
once saw was in the north, and we therefore knew that it 
was no star or planet which had so brilliant an appearance, 
and before the sunlight had sufficiently decreased to show a 
tail, we had decided that a remarkable comet must have 
come suddenly upon us. 
As the sun descended below the horizon and darkness 
stole over the scene, the comet’s tail became visible, and 
stretched from the nucleus, which was below the pole 
and near the northern horizon to far up above the zenith 
and over towards the south. By means of a pocket 
