COMETS. 27 



outer space would be arrested within finite limits by the gravitation of its particles. 



I am led to present the two sides of this question from a remark in a very- 

 able and interesting essay on Comets by Professor Lewis Boss, of the Dudley Ob- 

 servatory, published in the April number of the Kansas City Review of Science 

 AND Industry, where he states that "It is certain that no body entirely gaseous 

 could exist in space." 



With all due respect to the learned Professor I will say that science seems to 

 answer the question differently. It is, however, generally conceded that while 

 they are not composed entirely of gaseous matter, to some degree gas is present 

 in cometary structures. Again it has been ascertained that comets shine in some 

 degree by native and in some degree by reflected light, and the weight of scien- 

 tific opinion is in favor of regarding the bright nucleus as a solid or liquid body 

 in an incandescent state. Therefore, if we, for instance, suppose a comet freed 

 from that influence which produces its tail we would have a body consisting of a 

 glowing mass at the centre and surrounded by a highly attenuated substance shin- 

 ing partly by reflected light. 



This is in fact the shape to which comets generally approach as they recede 

 from the sun ; in which, it is believed, lies the agency which produces the tail. A 

 total ecHpse of the sun reveals that he is surrounded by a luminous envelope, to 

 which the name of " corona" has been given, which has been perceptible for a 

 distance of 850,000 miles from his surface. In addition to this, luminous stream- 

 ers have been observed proceeding in directions perpendicular to the surface of 

 the sun to a distance of nearly 2,000,000 miles, as if expelled by some active 

 force. Both corona and streamers have been found to shine partly by reflected 

 light. 



Taking this view of the sun we find it to consist of a glowing mass surround- 

 ed by an apparently gaseous substance shining in part by reflected light. This is 

 precisely the condition to which we reduced the comet by freeing it from the 

 agency which generates the tail. We may then reasonably carry the analogy 

 further and conclude that the nucleus of a comet corresponds to the photosphere 

 of the sun and that the nebulous envelope corresponds to the corona observed in 

 ecUpses. Also that as the phenomena of sun-spots indicate that within the shin- 

 ing photosphere of the sun is a darker mass which is in some manner protected 

 from intense heat, so there may be within the bright nucleus of a comet a similar 

 mass similarly situated and protected. 



When it is remembered that the great comet of 1680 was subjected to a tem- 

 perature of more than 2,000 times that of red-hot iron, a temperature capable of 

 dissipating any known substance, this supposition does not seem unreasonable. 

 Again, it is believed that the photosphere of the sun is composed of gas. If, then, 

 the bright nucleus of a comet is analogous to it, the latter must be inconceivably 

 less dense than the former, owing to the vast difference between the mass of the 

 sun and that of a comet, and this may explain why the nuclei of some comets 

 are transparent, and why they diminish in size with an increase of telescopic 

 power. Again, it is as yet a unanswered question as to what maintains the heat 



