motors provided for the purpose. When once directed toward the object to be observed it will frequently happen that the lower end of the telescope is far out of reach above the observer's head. For this reason the

Fig. 5.

The forty-inch telescope of the Yerkes Observatory.

entire floor of the observing room, 75 feet in diameter, is constructed like an electric elevator, which by throwing a switch can be made to rise or fall through a distance of twenty-three feet. Thus the lower end of the telescope is rendered accessible even for objects near the