Mounts, alt-azimuth and equatorial, 98 Myopia, glasses for, came slowly, 2 N Navicula Lyra, stages of resolution of, 271 Newton, abandoned parabolic mirror, 21 blunder in experiment, 20 gave little information about material for mirrors, 23 Isaac, attempt at a reflector, 20 Normal spectra, 190 O Objective, adjustable mount for, 44 adjusting screws of, 44 Clark’s form, 83 cleansing, 203 examination of, 202 Objective, four-part, 85 Fraunhofer flint-ahead, 83 how to clean, 216 spacers, to take out, 217 typical striæ in, 203 Objective prism, photographing with, 185, 187 Objectives, crown glass equiconvex, 80 over-achromatized, 90 rated on focal length for green 24 Observatories, cost of Romsey, 252 Observatory at small expense, 249 Romsey, description of, 249 with simple sliding roof, 245 Observing box, 229 Oblique fork alt-azimuth, 100 Ocular, apparent angular field of, 146 terrestrial, 147 Tolles terrestrial, 147 typical form, 45 Oculars, radius of curvature of image in, 146 undesirability of short focus, 275 Open fork mount, 115 well suited to big reflectors, 117 Optical axis, to adjust declination of, 238 Optical glass, classes of, 63 data and analysis of, 64 industry, due to single man, 36 production of, 60 Orthoscopic ocular, 145 P Parallactic mount, 104 Petition for annulment of Dolland’s patent, 29 Photometer, artificial star Zöllner, 194 extinction, 198 photoelectric cell, 199 precision of astronomical, 199 selenium cell, 199 Zöllner, 197 Photometers, three classes in stellar, 193 “Photo-visual, objective,” 89 Pillar-and-claw stand, 98 Pillar mount, 240 Pitch, optician’s, 71 Placement for tripod legs, 236 Polar and coudé forms of reflector, 125 axis, adjustment of by level, 232 axis, alignment to meridian, 232 axis, setting with finder altitude of, 234 telescope, 119, 122 Polaris, hour angle of, 233 a variable star, 199 Polarizing photometer, 193 Pole, position, 234 Polishing machine, 70 surface of tool, 72 tool, 71 Porro’s second form, 157 work, original description of, 156 Porta, description unintelligible, 7 Portable equatorial, adjustment of, 230 telescopes, mounting of, 228 Porter polar reflector, 130 Position angle micrometer of Lowell Observatory, 173 Powers, lowest practicable, 276 Prismatic inversion, Porro’s first form, 155 Prismatic inverting system, the first, 154 Prisms, Dove’s, 154 Prism field glasses, stereoscopic effect of, 159 Prism glass, 152 loss of light in, 160 objectives of, 161 weak points of, 160 R Resolving constant, magnification to develop, 275 power and verity of detail, 2 power of the eye, 274 Reticulated micrometer, 169 Reversion prism, 153 Right ascension circle, 108