ted in range; and quite a little series of operations has to be gone
through when it is required to direct the telescope towards a new
quarter of the heavens. However expert the observer may become by
practice in effecting these operations, they necessarily take up some
time (performed as they must be in the dark, or by the light of a small
lantern), and during this time it often happens that a favourable
opportunity for observation is lost.

These disadvantages are obviated when the telescope is mounted in such a
manner as is exhibited in fig. 8, which represents a telescope of my own
construction. The slow movement in altitude is given by rotating the rod
_he_, the endless screw in which turns the small wheel at _b_, whose
axle in turn bears a pinion-wheel working in the teeth of the quadrant
_a_. The slow movement in azimuth is given in like manner by rotating
the rod _h'e'_, the lantern-wheel at the end of which turns a
crown-wheel on whose axle is a pinion-wheel working in the teeth of the
circle _c_. The casings at _e_ and _e'_, in which the rods _he_ and
_h'e'_ respectively work, are so fastened by elastic cords that an
upward pressure on the handle _h_, or a downward pressure on the handle
_h'_, at once releases the endless screw or the crown-wheel
respectively, so that the telescope can be swept at once through any
desired angle in altitude or azimuth. This method of mounting has other
advantages; the handles are conveniently situated and constant in
position; also, as they do not work directly on the telescope, they can
be turned without setting the tube in vibration.

[Illustration: _Fig. 8._]

I do not recommend the mounting to be exactly as shown in fig. 8. That
method is much too expensive for an alt-azimuth. But a simple
arrangement of belted wheels in place of the toothed wheels _a_ and _c_
might very readily be prepared by the ingenious amateur telescopist; and
I feel certain that the comfort and convenience of the arrangement would
amply repay him for the labour it would cost him. My own
telescope--though the large toothed-wheel and the quadrant were made
inconveniently heavy (through a mistake of the workman who constructed
the instrument)--worked as easily and almost as conveniently as an
equatorial.

Still, it is well for the observer who wishes systematically to survey
the heavens--and who can afford the expense--to obtain a well-mounted
_equatorial_. In this method of mounting, the main axis i