510 



PHYSICAL SCIENCES. 



PHOTO-GALVANIC. 



Photo-galvanic engraving, 309. 



Photography, first suggestions, 203 ; 

 discoveries and improvements in, 

 204-207 ; conditions affecting the 

 chemical properties of rays pro- 

 ducing, 207, 208 ; images of the 

 solar spectrum obtained by, 208- 



210 ; coloured copy of an engraving, 



211 ; phenomena in, suggesting an 

 absorptive action in the solar at- 

 mosphere, 212, 213 ; chemical 

 energy producing, distinct from 

 light and heat, 214 ; experiments 

 by means of, testing the properties 

 of rays, 218, 219 ; experiments on 

 action of light, heat, electricity, 

 producing results analogous to ef- 

 fects of, 219-223. 



Photosphere, the, of the sun described, 

 224. 



Physical Sciences, the most extensive 

 example of their connection, mode 

 of its operation, 1. 



Pi Herculis, direction of solar motion 

 with regard to, 406. 



Pisces, nebulous region of, 417. 



Planetary motion, representation of, 

 14. 



nebula?, 409 ; appearance of, 



412. 



Planets, paths round the sun described 

 by, 5 ; law determining their revo- 

 lutions, ib. ; forces adjusting their 

 forms, 6 ; their motions in elliptical 

 orbits, mean distance from the sun, 

 8 ; mode of obtaining the place of, 

 in their orbits, 9 ; computations 

 giving the . place of, in space, 

 10 ; disturbances from reciprocal 

 attraction affecting, compensations, 

 13-19; telescopic, 20, 21; pertur- 

 bations in the mean motions of, 25, 

 26 ; influence of, on lunar motions, 

 36 ; eclipses and conjunctions of, 42 ; 

 formula finding their masses, 55 ; 

 their diameters, 56 ; mass of the 

 telescopic, compared with the moon, 

 ib. ; comparative density, 58 ; me- 

 thod of computing their places, 58- 

 64 ; discovery of, 61-63 ; exploded 

 theory touching telescopic, 63 ; pe- 

 riods of their rotations, 66 ; va- 



FOLARIZATIOX 



riation and position of the plane of 

 the ecliptic produced by, 79; its 

 effect on the equinoctial points, 80 ; 

 climates of, 225, 226 ; probably 

 magnets, 346 ; constant velocity of 

 their mean motions, 366. 



Plants, distribution of known species 

 over the globe, 249, 250. 



Plates, vibrating, experiments by means 

 of, 144-146. 



Plateau, M., experiments of, on colour, 

 165, 106. 



Platina, incandescent, used as a source 

 of heat, 260. 



Platinum, experiment producing spon- 

 taneous combustion of, 112, 113. 



Play fair, Professor, quoted in reference 

 to La Grange's discovery, 23. 



Pleiades, the, nebulous stars, 415. 



Pliicker, Professor, discoveries of, in 

 the action of magnetism in crystals, 

 349. 



Plumb-line, deviations of, from local 

 attraction, 48 ; earth's density cal- 

 culated from a deviation of, 58. 



Poinsot, M., La Place's discovery ex- 

 tended by, 23 ; comparison by, 24. 



Point, ready escape of electricity from 

 a, 288. 



Poisson, M., decisions of, on the phe- 

 nomena of capillary attraction, ) 14. 



Polar basin, probable temperature of, 

 245, 246. 



star, change of position in the, 



81,82. 



vegetation, contrasted with tro- 

 pical, 248. 



Polarity, produced by electricity, 282 ; 

 of magnets defined, 336 ; induced 

 in iron, 337 ; its antithetical mani- 

 festations of, 339 ; invariablv dual, 

 341 ; of diamagnetic substances, 

 347, 348. 



Polarization of light, definition of, 

 1 79 ; refracted by various sub- 

 stances, 180-183 ; by reflection, 

 184; angles of, 185; phenomena 

 exhibited by transmission through 

 analyzing media, 186-188; circular, 

 189-191 ; theory of circular and 

 elliptical, 192, 193 ; substances pro- 

 ducing, 193, 194; theory of co- 



