Note 3 — AN ACCOUNT OF THE CONSTRUCTION AND USE OF A SILVERED GLASS TELESCOPE.

Messrs. De La Rue and Nasmyth, who used one of Mr. Lassell’s machines, as I have since learned, met with the same trouble, and were led to make two additions to the mechanism: 1, to control the rotation of the polisher rigorously; and 2, to give the whole speculum a lateral motion, by which the intersecting points of the curves described by the polisher were regularly changed in distance from the centre of the mirror. Mr. Lassell had previously, however, introduced a contrivance for this latter purpose himself.