ASTRONOMY AND METEOROLOGY. 389 



The luminous phenomena resulting from this action, increase and decrease 

 in inverse ratios with the distance of the nucleus from the sun. 



The primary effect of this action is, to intensify the force of gravitation or 

 centralization among the particles of the comet; the secondary effect being 

 the evolution of light as a result of repulsion consequent upon the conflict 

 of this latter force with increasing condensation; both forces being excited 

 to more positive energy in the comet, by its approach to its perihelion. 



The luminous waves evolved by a comet are arrested by the luminous 

 waves projected from the sun, which latter seize upon, mingle with, decom- 

 pose, and sweep back the former into space, producing the tail. 



By this union, and reaction or decomposition of solar and cometary light, 

 a resplendency is communicated to the solar ray, which increases in visi- 

 bility and persistent power of extension into space, in direct ratios with the 

 commotion and repulsion excited within the comet, and inversely as the 

 square of its distance from the sun. 



The curvature apparent in a comet's tail is the resultant of compound mo- 

 tion; the first element being the comet's velocity through the perihelic arc 

 of its orbit; the second being the projection of luminous waves from the 

 comet, which are swept into space by solar action exerted at right angles to 

 the comet's path. 



These luminous waves are as independent of each other, and of the light 

 fountain from which they spring, as if they were particles of matter; and 

 being impelled into space by the undulations of solar light, the parts of the 

 resplendent train more distant from the sun become diffuse, since the veloc- 

 ity of the comet is leaving waves of light behind, which are constantly dis- 

 solving and vanishing in the great ethereal void. (This was explained by a 

 diagram.) 



Comets' tails, not being composed of particles of matter, but only of lu- 

 minous w r aves, rendered visible by decomposing causes, and possessed of no 

 angular velocity, have no such function as an orbit ; this becoming more cer- 

 tain, since the velocity of cometary light constantly varies, depending on the 

 fluctuating impulse of the solar wave, and modified every instant by the 

 repulsive energy within the nucleus, which generates the cometary waves. 



DENSITY AND CONSTITUTION OF COMETS. BY D. VAUGHAN. 



Although modern science has revealed the amount of matter contained in 

 the sun and the large planets, it has hitherto failed to furnish similar infor- 

 mation in regard to those celestial bodies which are too light to affect the 

 asti'onomical balance. Babinet has recently endeavored to ascertain the 

 density of conrets, from their effects on the brilliancy of the stars over which 

 they pass; and, as they have been generally incapable of causing any sensi- 

 ble diminution of stellar lustre, he concludes that cometary bodies, exceeding 

 the largest planets in size, can contain only a few tons of matter. This con- 

 clusion has been based on the fact, that our atmosphere is capable of render- 

 ing the faint stars invisible when it is illuminated by the light of the full 

 moon; while a far more extensive volume of cometary gases, though ex- 

 posed to the direct rays of the sun, fail to produce a similar effect. But we 

 may question the propriety of supposing that the power of gases to obscure 

 stellar light is in direct proportion to their density; and we have no grounds 

 for assuming that the nucleus is wholly destitute of all dense solid or liquid 

 matter. A globe of granite ten miles in diameter would weigh about 



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