Abney, spectrum map of.............................. 9,200 Absorption lines: Identification of.................................. 71,74,130 "Really" of........................................ 72 Absorption, selective............................... 11,215 Absorption, variations in........................... 205,264 Seasonal........................................... 207 Irregular.......................................... 207 Accidental deflections in records................... 105 Appropriation, Congressional........................ 3 Assistants, names and titles of..................... 2 Astrophysics, object of............................. 2 Battery, for bolometer.............................. 63 Becquerel, spectrum map of.......................... 9 Bolographic method: Description of..................................... 22,69 Errors inherent in................................. 119 Bolographs: Comparison of...................................... 129 Measurements on.................................... 137 Notes accompanying................................. 133 Ordinates of....................................... 159,210 Reduction of measurements on....................... 171 Bolometer: Accuracy of........................................ 238 Case............................................... 49,51 Circuit, best resistances of....................... 246 Description of..................................... 47 Invention of....................................... 10 Preparation of..................................... 48 Cauchy, dispersion formula.......................... 8,253 Clock, driving...................................... 25,56 Clouds, effect on bolographs........................ 111 Collimination, discussion of........................ 77,82 Comparator.......................................... 64 Measurements, accuracy of.......................... 118 Composite line spectra from bolographs.............. 73 "Cylindrics"........................................ 37,116 Diffraction, energy lost by......................... 79 Dispersion formulae................................. 253 "Drift" of galvanometer............................ 12,22,107 Error, sources of.................................. 86,122,125 Fluorite, dispersion of............................ 219,221,258 Galvonometer: Coils, construction of............................. 248 Description of................................... 17,24,30,59,244 Needle, construction of............................ 251 Sensitiveness...................................... 17,25,30,60,251 Suspension......................................... 62 Grating, constants of............................... 225 Herschel, Sir J..................................... 8 Higgs, spectrum map of.............................. 200 Identification of absorption lines.................. 71,74,130 Infra-red solar spectrum: Illustrations of................................... 127 Mapping of......................................... 126 Julius, W. H., method of suspension................. 38,62 Kayser and Runge, formula for spectrum series....... 19 Ketteler, dispersion formula........................ 254,260,261 Lamansky, M. S...................................... 8 Latitude and longitude of observatory............... 4 Lens, cylindric..................................... 67,116 Lewis, E. P......................................... 20 Light, cheapest form of............................. 3 Mechanism, accuracy of.............................. 112 Melloni............................................. 7 Minimum deviation................................... 88,92 Mirror, cylindric................................... 82 Mount Whitney....................................... 13,23,127,200 Nichols, E. F....................................... 21 Observatory: Description of..................................... 40 Early annals of.................................... 3 Founding of........................................ 1 Paschen, F.......................................... 18,120,222,256,258 Photographic room................................... 28 Plate carrier....................................... 58 Prism............................................... 45,56 Aberration of...................................... 78 Angle determination of............................. 92,173 Concavity of faces................................. 89 Resolving power of................................. 76,82 Radiation from terrestrial sources.................. 240 Rayleigh, Lord...................................... 76,78 Refractive index of A............................... 172 Resolution: Bolometric......................................... 82 Visual............................................. 76 Rheostat, special for bolometer..................... 38,50,51 Rock salt........................................... 14,28 Dispersion of...................................... 16,219,222,233,236,255,261 Apparatus for determining.......................... 224 Methods of determining............................. 226 Prisms as standards of dispersion.................. 236 Thermal conductivity of............................ 102 Rubens, H........................................... 18,256,259 Shop, instrument making............................. 4 Siderostat, Grubb................................... 23,45,65 Slit................................................ 46,65 Snow, B. W.......................................... 20 Spectrobolemeter.................................... 30,43,46 Spectrum, infra-red solar........................... 5,15,23,198,205 Tables of infra-red solar absorption lines.......... 177,188,198 Temperature and deviation........................... 96,100,101 Temperature, changes errors from.................... 26,94,104 Temperature control, automatic...................... 41,95 Very, F. W.......................................... 18 Wave-lengths of infra-red solar absorption lines.... 175,198 Welsbach mantles, radiation of...................... 240,242 Wind, remarkable penetration of..................... 108