XIV CONTENTS. 



284. Cooling by radiation and convection: very small pressures 252 



285. temperature and pressure effect 252 



286. Conduction of heat across air spaces, ordinary temperatures .... 253 



287. Convection of heat in air at ordinary temperatures 253 



288. and conduction of heat by gases at high temperatures: . 254 



(a) s as function of a/B 254 



(b) <j) in watts per cm. as/(rK) 254 



289. Heat losses from incandescent filaments: 255 



(a) Wires of platinum sponge 255 



(b) " " bright platinum 255 



THE EYE AND RADIATION 



290. Spectral variation of sensitiveness as function of intensity (Lumina- 



tion intensities under various circumstances) 256 



291. Threshold sensibility as related to field brightness 256 



292. Heterochromatic threshold sensibility 257 



293. Contrast or photometric sensibility 257 



294. Glare sensibility 257 



295. Rate of adaptation of sensibility 257 



296. Apparent diameter of pupil and flux density at retina 258 



297. Relative visibility of radiation of different wave-lengths 258 



298. Miscellaneous eye data: physiological; persistence of vision; sensi- 



bility to small differences of color; flicker 258 



PHOTOMETRIC TABLES 



299. Photometric definitions and units 259 



300. standards 260 



301. Intrinsic brightness of various light sources 260 



302. Visibility of white lights 260 



303. Brightness, Crova wave-length, mechanical equivalent of light . . . 261 



304. Luminous and total intensity and radiant luminous efficiency of a 



black-body; minimum energy necessary for light sensation ... 261 



305. Color of light emitted by various sources 261 



306. Efficiency of various electric lights 262 



PHOTOGRAPHIC DATA 



307. Numerical constants characteristic of a photographic plate 263 



308. Relative speeds of various photographic materials 263 



309. Variation of resolving power with plate and developer 263 



310. Photographic efficiencies of various lights 264 



311. Relative intensification of various intensifiers 264 



SPECTRUM WAVE-LENGTHS 



312. Wave-lengths of the Fraunhofer lines 265 



313. Standards: Red cadmium line, 76 cm, 15 C, Angstroms 266 



