Note 58 — Chapter XV · THE WONDERS OF THE REFRACTION OF LIGHT (continued).

Within the last 30 years the diamond has been used for the purpose of microscopic lenses; for, owing to the refractive power of this precious stone being greater than almost any other known substance, and nearly double that of glass, lenses can be produced from it of a great degree of magnifying power, and that with a comparatively small curvature, so that increased distinctness is obtained; while the lens itself, being nearly “achromatic,” the image produced by it is untinged by prismatic colours. Mr. Pritchard constructed the first diamond microscope in 1826. The diamond lens of this was double convex, and had a focus of ¹⁄₃₀th of an inch, so that its magnifying power was 150 times. Dr. Goring, an eminent authority on the subject, says—“I conceive diamond lenses to constitute the ultimatum of perfection in the single microscope.” The sapphire has also been used for the construction of microscopic lenses with considerable advantage, its magnifying power being much greater than that of glass. Mr. Pritchard says, that the sapphire, next to the diamond, possesses all qualities requisite for the formation of a perfect magnifier, and presents less difficulties in the construction.