288 The Pole Star and the Pointers. (July, 
circle which cuts the east and west points of the horizon, 
and passes through the pole of the heavens. This circle 
the reader, on reflection, will perceive must be a circle at 
right angles to the equino¢ctial, and its trace in the sky would 
be as follows :—Starting from the east point of the horizon, 
this circle would trace an arch in the heavens the highest 
part of which would be at the pole, when its altitude above 
the horizon would be equal in degrees and minutes to the — 
latitude of the place of observation ; the curve would con- 
tinue its arch-like form, and would cut the western point of 
the horizon. This curve or arch traced in the sky by a 
great circle passing through the pole, and cutting the east 
and west parts of the horizon, vem appear as shown in the 
following diagram. 
In this diagram N represents the north portion of the 
horizon, P ane pole of the heavens, E the east and wthe | 
west points on the horizon, whilst the curve E P W shows 
FIG. 2. 
P 
w 
the curve or arch traced by a great circle in the sky, which 
great circle is at right angles to the equino¢tial, and cuts the 
east and west portions of the horizon. 
The reader may perhaps wonder what these arches have 
to do with the pole star and the pointers: they have every- 
thing to do with them, and in fact are the key to this and to 
other mysterious problems which seem to have hitherto 
greatly perplexed some persons, for both this and the pre- 
ceding arch are in reality straight lines, though they appear as 
curves to us; for both this curve and the arch traced by the 
equinoctial would appear like straight lines to a person at 
the north pole of the earth, the equino¢tial there appearing 
coincident with the horizon, and therefore like a straight 
line, the curve E P W appearing like a vertical line and as 
straight as a plumb-line. 
We will now place relatively to the curved line WPE 
three stars, and show what would be the relative changes 
