486 



PHYSICAL SCIENCES. 



COAL. 



"Coal Sacks" in the Milky Way, 

 386. 



Cohesion, influence of, on matter, 105 ; 

 phenomena arising from its force, 

 106 ; attraction of, overcome by 

 the expansive power of heat, 271. 



Cohesive force, properties of material 

 molecules constituting, 103 ; ef- 

 fectual only to unite particles of 

 like nature, 110; inducing chemi- 

 cal combination, 112 ; capillary 

 attraction, an action of, 113. 



Coins, impressions taken from, by 

 contact, 220; by electricity, 221. 



Cold, contraction caused by, 271, 

 272 ; mitigated by slow propaga- 

 tion of heat in air, 273 ; generated 

 by voltaic electricity, 302 ; in- 

 creasing the conducting power of 

 the air, 345. 



Colladon, M., experiments of, testing 

 the velocity of sound, 135. 



Collision between the earth and 

 comets, possibilities, possible effects 

 of, 367, 369. 



Collodion, sensitiveness of, to light, 

 203 ; properties of, as an agent in 

 photography, 207. 



Colours, seven primary, 159 ; theory 

 of the decomposition of white 

 light into, 160 ; degree of re Iran - 

 gibility not invariable, 161 ; three 

 primary, ib. ; new, discovered by 

 Sir John Hersehel, 162 ; rays re- 

 fracted without, 164; rarely ho- 

 mogeneous, 165 ; experiments on 

 accidental and complementary, 165, 

 166 ; determined by undulations of 

 ether, experiments, 170-175 ; of 

 material substances, whence de- 

 rived, 175 ; produced by analyzing 

 polarized light, 186-188; varying 

 with refrangibility of rays, 198 ; 

 obtained in photography, 206 ; 

 images of the solar spectrum imi- 

 tating the prismatic, 208-209 ; of 

 seaweeds, 253 ; not invariably 

 dependent on light, ib. ; affected by 

 absorption and reflection, 268 ; of 

 the electric spark, affected by the 

 atmosphere, 289; of the voltaic 

 spectrum, 303; of the electric 



COMPASS. 



spark, 304 ; produced by oxidation 

 on silver, 305 ; of the fixed stars, 

 401, 402; of planetary nebulae, 

 412 ; of nebulous clusters, 415. 



Columbus, beds of alga? found by, 

 253. 



Column, capillary, forces producing 

 changes in its form, 114, 115. 



Coma Berenices, a nebulous cluster, 

 415 ; nebulous zone passing, 416, 

 417. 



Combustion, cause of, 270 ; defined, 

 304. 



Comets, attraction by the sun of, 5 ; 

 disturbances in the motion of, a 

 key to the nature of the ethereal 

 medium, 22 ; retrograde motion in, 

 33 ; passing through Jupiter's sa- 

 tellites, 69; return of, to their 

 perihelia, furnishing historical data, 

 88 ; existence of the luminous ether 

 demonstrated by, 168, 169 ; terres- 

 trial atmosphere unaffected by, 

 358 ; amount of their light com- 

 puted, 358, 359 ; passages of, 

 through the solar system, 359 ; 

 velocity, paths of, 359', 360 ; proof 

 of the return of, 360 ; disturbing 

 action of planets on their orbits, 

 361; of 1770, an example, 361, 

 362 ; computed return of Hal ley's, 

 362, 363 ; aspects, records of 

 Halley's, 363-365 ; discoveries made 

 by the revolutions of, 365 ; of the 

 solar system, Encke's, 365, 366 ; 

 Biela's, possibility of collision with, 

 367, 370 ; periods of various, 370 ; 

 cause of their brilliancy, 371 ; ve- 

 locity, sun's influence on, 371, 372 ; 

 of 1843, 372, 373 ; their constitu- 

 tion, 373, 374 ; of 1811, its lu- 

 minous envelopes, 374, 375 ; sud- 

 den convulsions in, 375 ; tails, 

 375-377 ; causes assigned for con- 

 traction of diameter in, 377, 378 ; 

 Donati's, 378, 379 ; nature of their 

 light, 379-381 ; computations of 

 their numbers, 381, 382; orbits 

 of, 383 ; nebula resembling, 413. 



Compass, mariner's, phenomena dis- 

 turbing, 312 ; intensity of a gal- 

 vanic current measured by, 315. 



