Having found the seven stars, we make use of the pointers [alpha] and [beta] (shown in Plate 1) to indicate the place of the Pole-star, whose distance from the pointer [alpha] is rather more than three times the distance of [alpha] from [beta].
Now stand facing the Pole-star. Then all the stars are travelling round that star _in a direction contrary to that in which the hands of a watch move_. Thus the stars below the pole are moving _towards the right_, those above the pole _towards the left_, those to the right of the pole _upwards_, those to the left of the pole _downwards_.
Next face the south. Then all the stars on our left, that is, towards the east, are rising slantingly towards the south; those due south are moving horizontally to the right, that is, towards the west; and those on our right are passing slantingly downwards towards the west.
It is important to familiarise ourselves with these motions, because it is through them that objects pass out of the field of view of the telescope, and by moving the tube in a proper direction we can easily pick up an object that has thus passed away, whereas if we are not familiar with the varying motions in different parts of the celestial sphere, we may fail in the attempt to immediately recover an object, and waste time in the search for it.
The consideration of the celestial motions shows how advantageous it is, when using an alt-azimuth, to observe objects as nearly as possible due south. Of course in many cases this is impracticable, because a phenomenon we wish to watch may occur when an object is not situated near the meridian. But in examining double stars there is in general no reason for selecting objects inconveniently situated. We can wait till they come round to the meridian, and then observe them more comfortably. Besides, most objects are higher, and therefore better seen, when due south.
Northern objects, and especially those within the circle of perpetual apparition, often culminate (that is, cross the meridian, or north and south line) at too great a height for comfortable vision. In this case we should observe them towards the east or west, and remember that in the first case they are rising, and in the latter they are setting, and that in both cases they have also a motion from left to right.