The toothed wheels give a slightly better efficiency, but the worm gear is somewhat smoother in its action and entirely silent; the noise of gearing can, however, be considerably reduced by careful machining of the teeth, as is now always done, and also by the use of pinions made of rawhide leather or other non-resonant material.
In electric cranes the motor is connected to the barrel, either in a similar manner by spur gear or by worm gear.
These have a speed reduction from armature shaft to bridge column of 1500 to I, through four intermediate spur gears and a worm gear.
The driving clock moves the telescope in right ascension by means of a worm-gear wheel, 10 ft.
A worm-gear tackle of this description is shown in fig.
