ASTRONOMY AND METEOROLOGY. 329 



decomposable by the solar light, the visible head and tail being an 

 actinic cJoud resulting from such decomposition. The tail is not 

 matter projected from the head, but matter precipitated on the 

 solar beams which traverse the cometary atmosphere ; nothing 

 being carried from the comet to form the tail, but something be- 

 ing deposited from the interplanetary sj^ace through which the 

 body is coursing. But this explanation supposes that the sunlight 

 has a different power when it has passed through a vapory comet 

 to that which it possesses when it has traversed no such medium ; 

 otherwise all space would be lit up like a comet's tail. To account 

 for such a peculiar property, Prof. Tyndall assumes that the sun's 

 heating and chemical powers are antagonistic, and that the calo- 

 rific rays are absorbed, more copiously by the head and nucleus 

 than the actinic rays. This augments the relative superiority of 

 the actinic rays behind the head and nucleus, and enables them to 

 bring down the cloud which constitutes the tail. Thus the caudal 

 appendage is in a perpetual state of renovation as the comets 

 move through space ; the old tails being dissipated by the solar 

 heat as soon as the}^ cease to be screened by the nucleus. Nearly 

 all the phenomena observed in those mysterious bodies are ac- 

 counted for by Dr. Tyndall. One, however, he has not men- 

 tioned ; namely, the peculiar luminous envelopes, familiar to 

 comet-gazers, which surround the nucleus like a series of cloudy 

 glass cases. No theory can be called complete which does not 

 account for those remarkable and evidently important features. 



COMETS. 



M. Bionne has submitted the following opinion upon the nature 

 of comets to the Academy of Sciences: "Comets are bodies 

 which describe spirals originating in a nebula terminating in the 

 sun ; each spiral may be considered as an ellipse. . Formed of the 

 incandescent matter of the nebuliB, comets would appear to be 

 the resrulators of the grand movement of celestial bodies, the 

 a2:ents of tliat vast transformation of calorihc work into mechani- 

 cal work, and would come at the end of their course to lose them- 

 selves in the atmosphere of the sun, to which they would serve as 

 an aliment." 



winnecke's comet. 



Huggins' spectral analysis of this comet is well known, and his 

 conclusion that the light of this comet is produced by incandescent 

 carbon vapor. The experiments of -Watts, published in "The 

 Philosophical Magazine," seem to prove that this spectrum is 

 really that of carbon; and, further, that the temperature of the 

 carbon producing it must bo between 1,500° C. and 2,o00° C. If 

 no other explanation of this comet spectrum can be found, and if 

 the temperature of cosmical space may really reach 1,500° C, im- 

 portant changes must be made in the theories of the universe as 

 at present accepted. — The Academy, Nov. 12, 1869. 



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