Note 6 — Chapter II · LIFE OF THE BROTHER AND SISTER IN BATH.

“The grinding of specula used to be performed by the hand, no machinery having been deemed sufficiently exact. The tool on which they were shaped having been turned to the required form, and covered with coarse emery and water, they were ground on it to the necessary figure, and afterwards polished by means of putty or oxide of tin, or pitch spread as a covering to the same tool in the place of the emery. To grind a speculum of six or eight inches in diameter was a work of no ordinary labour; and such a one used to be considered of great size.”—“Lord Rosse’s Telescopes,” 1844.