Tests for striæ and annealing, 68 Transparency, lack of in atmosphere, 255 Triplet, cemented, 85 Turret housing of reflector, 244 V Variable stars, 192 W Wedge calibrated by observation, 197 photographic, 197 photometer, 197 Wind, shelter from, 240 Z Zeiss, binocular of extreme stereoscopic effect, 161 Zöllner, photometer modification of, 198 Zonal aberration, 209 * * * * * Transcriber's Notes Obvious typographical errors have been silently corrected. Variations in hyphenation and accents have been standardised but all other spelling and punctuation remains unchanged. Italics are represented thus _italic_, bold thus =bold=, subscript thus _{s} and underline thus underline=. In caption of Fig. 49.—Spherical Aberration of Concave Lens. Concave has been changed to Convex In “An objective of 4.56′ inches aperture has a resolving constant of 1″ and to develop this should take a magnification of say 300,” 1″ has been hand altered in the original and may be 1′. The table “Characteristics of Optical Glasses″ has been divided to fit within the width restriction. End of the Project Gutenberg EBook of The Telescope, by Louis Bell