Note 7 — AN ACCOUNT OF THE CONSTRUCTION AND USE OF A SILVERED GLASS TELESCOPE.
Reading edition
A right-angled prism cannot be used with advantage to replace the plane silvered mirrors, because it transmits less light than they reflect, is more liable to injure the image, and the glass is apt to be more or less colored. Its great size and cost, one three inches square on two faces being required for my purposes, has also to be considered.