The machine in question consists of a revolving sheave or ring, with a sliding strip across its diameter; the said strip having a slot and clamping screw at one end, and a hole towards the other, through which passes the axis of the tool used in forming the lens,—the slot in the strip allowing the tool to give any stroke from 0 to 1.25 inch. 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. We hope, at some future time, for a special detail of Mr. Lancaster's interesting investigations, from his own mind and pen.
[12] The translations are made by W. Cadwalladr Davies, Esq.
[13] This evidence was given by Mr. W. Cadwalladr Davies on the 28th October, 1880.