504 



PHYSICAL SCIENCES. 



MEDIUM. 



tion, 358 ; unsolved question 

 touching, 365; a cause of accele- 

 rated revolutions of comets, 366, 

 367 ; direction of its increase in 

 density, 367. 



Medium occupying space, 424. 



Medusa tribes, the, phosphorescent 

 brilliancy of, 295. 



Megallanic clouds, the, 417, 418. 



Melloni, M., experiments of, in pho- 

 tography, 214; his application of 

 the principle of thermo-electricity, 

 333 ; experiments of, in transmis- 

 sion of heat, 258-263 ; fixing the 

 maximum of heat in the solar spec- 

 trum, 264 ; in polarization of heat, 

 264-266 ; light separated from 

 heat by, 265. 



Melville Island, height of the ther- 

 mometer in, in January, 247. 



Mercury, inclination of his orbit to 

 the plane of the ecliptic, 21 ; eclipse 

 of, 42; cause of his rotation un- 

 known, 65 ; ellipticity of his orbit 

 compared with the terrestrial, 74 ; 

 climate of, 226 ; comet revolving 

 between the orbits of Pallas and, 

 367 ; attraction of, determining a 

 comet's orbit, 369 ; comets revolv- 

 ing in his orbit, 381 ; velocity of, 

 400. 



, propagation of heat in, 273 ; 



rotating by electricity, 314. 



Meridian, constant, of high water, 92. 



, mode of determining the mag- 

 netic, 343. 



Meridians, size and form of the earth 

 determined from, 46 ; measurement 

 of arcs, 47 ; anomalies from local 

 attraction, 48 ; result of the com- 

 putations, 48, 49 ; permanent, of 

 the moon, 69, 70. 



, magnetic, influencing the direc- 

 tion of metallic veins, 346. 



Messier, comet of 1770 observed by, 

 361 ; Encke's comet seen by, 365 ; 

 nebula described by, 409. 



Metallic salts, action of the rays of 

 the solar spectrum on, 203. 



springs used in construction of 



musical instruments, 143 ; rods 

 giving musical notes, 144. 



MITSCHERL1CH. 



Metallic surfaces, polarized light re- 

 flected from, 193 ; plates, impres- 

 sions on, from bodies in contact with, 

 220. 



Metals, expansion of, by heat, 271 ; 

 propagation of heat in, 274 ; trans- 

 mission of electricity by, 284 ; elec- 

 tricity developed by oxidation of, 

 298 ; determining the appearance 

 of a spectrum of voltaic flame, 303 ; 

 distilled in the voltaic arc, 304, 

 305 ; electro-plating of, 309 ; pro- 

 perties of, modifying electric suscep- 

 tibility, 333 ; magnetism an ageut 

 in the formation of, 346. 



Meteor, the bursting of a, 118. 



Meteors, 420 ; theory of, 421-423. 



Meteoric stones, proofs of their foreign 

 origin, 420, 421 ; shower of, 421, 

 422. 



Metre, adopted by the French as their 

 unit of linear measure, 89. 



Mica, polarization by induction effected 

 with, 286. 



Milky Way, the, described, 385 ; Sir 

 John HerscheFs description, 385, 

 386 ; " Coal Sacks," 386 ; stars 

 composing, 286, 287 ; zone of stars 

 crossing, 390 ; position of variable 

 stars with regard to, 395 ; crowd- 

 ing in, apparent only, 405 ; orbit 

 in the plane of, 406 ; relation of, to 

 the stellar universe, 407 ; nebula 

 resembling, 409 ; its quarter of the 

 heavens, 414, 415 ; dividing the 

 nebulous system, 416, 417 ; great 

 nebula in, 418 ; remote branches of, 

 419. 



Minerals, possessing the phosphores- 

 cent property, 294. 



Mines, cause of increased temperature 

 in, 229 ; green plants growing in, 

 253. 



Mira, periods of its fluctuations in 

 lustre, 390. 



Mirage, supposed cause of, 157. 



Miraldi, rotation of Jupiter's satellite 

 determined by, 70. 



Mitscherlich, M., his experiments on 

 crystals, 107 ; discoveries, 108 ; ex- 

 periments of, in expansions of crys- 

 tals, 272. 



