Crossword-Solution: ACHROMATIC 10 letters, 39 clues 🏆 scrabble score: 19

They should be achromatic, and the utmost transparency should be obtained; and under the closest inspection of the glass not the slightest wavy appearance, or dark spot should be detected; and a curvature which as much as possible prevents spherical aberration should be secured.

Achromatic lens (Opt.), a lens composed usually of two separate lenses, a convex and concave, of substances having different refractive and dispersive powers, as crown and flint glass, with the curvatures so adjusted that the chromatic aberration produced by the one is corrected by other, and light emerges from the compound lens undecomposed.

See Prism, Ð Achromatic telescope, or microscope, one in which the chromatic aberration is corrected, usually by means of a compound or achromatic object glass, and which gives images free from extraneous color.

And in course of time, by his rare and exquisite manipulative skill, he succeeded in constructing a four-inch refractor, or achromatic telescope, of admirable defining power.

Since the discovery by Dollond, in 1758, of the relation between the refractive and dispersive powers of different kinds of glass, and the invention by that distinguished optician of the achromatic telescope, the manufacture of that instrument had been confined to England, where the best flint glass was made.