1874.] The Pole Star and the Pointers. 287 
the sphere of the heavens lines that of course cannot be 
drawn there. 
The first problem that we shall submit to the reader refers 
to the apparent course of the sun in the heavens, from its 
rising to its setting on the 21st of March. 
We will suppose that a person is situated at a locality in 
52 north latitude, and facing the south. At 6 o'clock in the 
morning on the 21st of March the sun would rise above the 
eastern point of the horizon, trace a curve or arch in the 
heavens, until at the south it would attain an elevation above 
the horizon of 38°. When exactly south the sun would 
move nearly horizontally for a short part of its course; it 
wouid then gradually descend, slowly at first, but more 
rapidly afterwards, and at 6 o’clock p.M. would set below the 
western point of the horizon. 
If we could mark out on the heavens the course traced by 
the sun, as stated above, we should draw a curve similar to 
HS Rin the annexed diagram. In this diagram the horizon 
Fig. 1. 
H o R 
is represented by the straight line HOR, H being the east, 
0 the south, and Rr the west points on the horizon. s would 
be the position of the sun relative to HOR when the sun 
was south, and the arc OS, representing the sun’s altitude, 
would be 38°. 
It will be seen that, if we could sketch or mark on the 
sky the course traced by the sun, this course would appear 
to us a great arch, as shown by HSR. 
Now this arch traced by the sun on the 2ist of March 
is the position which the earth’s equator would occupy if 
produced to the distant sky, and this arch is termed the 
equinoctial. The equinoctial therefore cuts the east and 
west points of the horizon, traces a curve in the heavens, 
and at its south point is as many degrees above the horizon 
as go exceeds the latitude of the place of observation. 
We will now suppose that the observer turns round and 
faces the north, and traces out on the sky the half of a great 
