The lens is carried on a revolving turn-table, with an arrangement to allow the axis of the lens to coincide with the axis of the table.

The ratio of speed between the sheave and turn-table is arranged by belt and properly sized pulleys, and the whole can be driven either by hand or by power.

The sheave merely serves as a guide to the tool in its path, and the lens may either be worked on the turn-table or upon a chuck attached to the tool rod.

The work upon the lens is thus to a great extent independent of the error of the machine through shaking, or bad fitting, or wear; and the only part of the machine which requires really first-class work is the axis of the turn-table, which (in this machine) is a conical bearing at top, with steel centre below,--the bearing turned, hardened, and then ground up true, and run in anti-friction metal.

Other details might be given, but these are probably enough for present purposes.