390 ANNUAL OF SCIENTIFIC DICOVERY. 



6,000,000,000,000 tons; yet in the nucleus of most observed comets, such a 

 mass would not be readily distinguished, even by the most powerful 

 telescopes. 



If we endeavor to estimate the attractive power of comets from its effi- 

 ciency in holding their parts together in certain regions of the solar system, 

 it would seem that they must contain far more matter than Babinet assigns 

 to them. The tidal force of the sun, or the disturbing action which he exerts 

 on the surface of one of his attendants, is inversely proportional to the den- 

 sity of the latter multiplied by the cube of its distance. On our own globe 

 this solar disturbance amounts to aiy.u^V.uu^ ^ terrestrial gravity. If the 

 earth's attraction were 20,000,000 times as feeble as it is at present, bodies 

 could have no weight at those places in conjunction and in opposition with 

 the sun, and the planetary form could no longer be preserved. Had a comet 

 8,000 miles in diameter, moved in a circular orbit, at a distance of 95,000,000 

 from the sun, it could not resist his dismembering effects, unless it were at 

 least equal to ^ Tj-.iyo'V.TTo'U' ^ ^ e terrestrial mass, and contained over 

 300,000,000,000,000 tons of matter. Had such a comet revolved in the orbit 

 of Neptune, the attraction of 10,000,000,000 tons of matter would be sufficient 

 to maintain its integrity. 



These results, however, are obtained on the supposition that gravity is the 

 only power concerned in keeping the cometary matter together; but it would 

 seem that some other agent is employed to secure the same end. The head 

 of the comet of 1811 was over a million of miles in diameter, and the attrac- 

 tion of a nucleus equal in mass to the planet Mercury, would be scarcely 

 adequate to preserve the stability of so extensive a body during its perihe- 

 lion passage. Yet, according to them easurements of Herschel, the diameter 

 of the nucleus was little over 400 miles, and it would seem that the sur- 

 rounding nebulous matter was too rare to compensate for the defective 

 attractive power of so small a globe. Even a few comets of considerable 

 size pi-esent scarcely any indications of the presence of dense solid or liquid 

 matter in their central regions ; and it may be interesting to inquire whether 

 the constitution of comets, and the peculiar phenomena which they exhibit, 

 may not, as Dr. Winslow supposes, be ascribed to the agency of electricity 

 or magnetism. By tracing the legitimate consequences of electrical action, 

 as manifested on our globe, we may easily account for the preservation of 

 these celestial wanderers in the vicinity of the sun, without altering or modi- 

 fying, in any degree, the doctrines now held by astronomers respecting uni- 

 versal gravity. 



Several observations show that the uppermost regions of our atmosphere 

 are most highly charged with electricity ; and this is sufficient to create an 

 attraction between the earth's surface and the higher strata of air, so as to 

 render atmospheric pressure a little greater than could arise from terrestrial 

 gravity alone. Were the earth deprived of this gravitative power, the air 

 would be confined around its surface by electrical action, and would be pre- 

 vented by this feeble tie from retiring into space, though it might swell to a 

 height of many thousand miles. There can be little doubt, that the elec- 

 trical conditions of the envelop or atmosphere of a comet would hold it to 

 the central nucleus, independent of any gravitative power which the latter 

 may exert. On our planet, the solar heat is the main source of atmospheric 

 electricity, as it gives rise to evaporation, and by putting the winds into mo- 

 tion, causes the friction of the air against the land and water. By these 

 operations electric forces are continually called into existence. If heat is 



