350 



INDEX. 



Playfair. See Jonle 

 Porcelain, radiation of, 242, 243 

 Position, energy of, 110, 131 

 Potential energy, 110, 111 et set)., 129, 



130, 199 

 Pouillet's method of measuring expansion 



of bars, 20 ; researches on the sun's 



radiation, 251-252 

 Pressure, influence of, on volume of gas, 



41 ; of gases, 134 ; relation of, to 



the boiling-point, 163-181 

 Pringsheim, on spectra of gases, 156. 



See also Lummer 

 Pyrheliometer, 251 



QUABTZ, heat conductivity of, 101 



RADIANT energy, 113, 129, 131, 221 et seq. 



Radiation, denned, 88, 113, 220-236; 

 radiant energy, 220; radiometers, 

 220; thermopile, 221 ; radio-micro- 

 meter, 221-222 ; bolometer, 222 ; 

 radiant energy similar to light, 222, 

 224; wave-length range of radiant 

 energy, 224-225 ; radiometers mea- 

 sure energy only, 225-226 ; emissive 

 powers, 226, 227 ; different wave 

 lengths in, 227-228 ; absorptive 

 powers, 228-230 ; reflecting powers, 

 230; diffusion, 231 ; general results, 

 231-233; deposition of dew, 233; 

 formation of ice, 233-234 ; by gases 

 and vapours, 234-236 ; theory of 

 exchanges of, 237-243; and tem- 

 perature, 244-257 ; variation of rate 

 of, with temperature, 244-245 ; 

 Newton's law of cooling, 245-246 ; 

 Dulong and Petit's law of, 246-248 ; 

 Rosetti's law, 248 ; Stefan's law, 

 248-250 ; constants of, 250 ; radiation 

 from surfaces which absorb selec- 

 tively, 250-251 ; the solar constant, 

 251-257; source of solar energy, 

 257; thermodynamics of, 333-342; 

 the pressure of, 334 ; the normal and 

 the total mean of, 334-335 ; pressure 

 on a fully radiating surface, 335 ; 

 relation between energy density 

 and temperature in full, 335, 337 ; 

 full radiation unaltered in adiabatic 

 change, 337-338 ; relation between 

 volume and temperature, 338 ; en- 

 tropy, 338 ; application of Doppler's 

 principle, 338-340 ; change of energy 

 in, 340-341 ; distribution of energy 

 in the spectrum, 341-342 



Radiometer, 135, 149, 150, 151, 220; 

 measures radiant energy only, 225- 

 226 



Radiomicrometer, 221-222 



Railways, expansion of steel by heat in, 

 17, 24, 25 



Raindrops, rate of fall of, 217-218 



Ramsay and Young, on vapour pressure 

 of ice and water, 173, 312 ; on 

 critical constants, 192 



Ramsden's method of measuring linear 

 expansion of metals, 18, 19 ; modi- 

 fied form, 19, 20 



Raoult, on boiling-points and vapour 

 pressures of solutions, 321, 323 



Rayleigh, on gas densities, 176 



Reaumur scale, 5 



Red heat, temperature of, 12 



Red lead, emissive power of, 226 



Reduced isothermals, 195-196 



Reflecting powers of surfaces, 230 



Refractive index, relation of, to the 

 critical point, 192 



Refrigerator, 261 



Regelation, 201-203 



Regenerative method of liquefying gases, 

 198 



Regnault's experiments on expansion of 

 mercury with heat, 31-35; of gas 

 with rise of temperature under con- 

 stant pressure, 42-44, 118-119 ; 

 increase of pressure with rise of 

 temperature and constant volume, 

 44-46, 118, 119 ; normal air thermo- 

 meter, 48 ; experiments by, on 

 specific heat, 68-71, 77, 80, 127, 181 ; 

 on Dulong and Petit's law, 86, 87 ; 

 on molecular heat, 86 ; on vapour 

 pressure of water, 172-175, 310 et 

 seq. ; on vapour densities, 176, 213- 

 215 ; on latent heat of steam, 179- 

 182 ; on the critical constants of 

 gases, 191 ; dew-point apparatus of, 

 209-210 ; density of water-vapour, 

 213 ; on vapour pressure of ice, 310 

 et seq. 



Relative humidity, 209 et seq. 



Reversible cycles, 272 et seq. 



Reversible heat engines, 262 et seq. 



Reynolds, on thermal transpiration, 142 ; 

 on the radio-thermometer, 150 



Reynolds and Morby, on the mechanical 

 equivalent of heat, 126, 127 



Richard. See Jam in 



Ring vortex theory of atoms, 131 



Rock-salt, absorption of radiant energy 

 by, 225-243 ; refractive index of, 

 227 ; radiation transparency of, 234 



Rontgen, on specific heats of air, 293 



Rosetti's law of radiation, 248 ; observa- 

 tions on solar radiation, 225, 256 



Rotch, on exploration of air with kites, 

 218 



Rowland, on specific heat of water, 77- 

 78, 80, 127 ; on the mechanical 

 equivalent of heat, 124, 125, 127, 128 



Rudberg, method of determining volume 

 expansion of gas with rise of tem- 

 perature under constant pressure 

 42-43 



