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.