tamly seems natural to expect that these cosmical bodies might 

 give us some insight into the nature of the forces in operation 

 at the sun's_ surface. It is assuredly too late to urge that the 

 transformations whicli thej undergo under the sun's influence 

 arc wholly involved in mystery ; for it has certainly been satis- 

 factorily established that a portion of the cometary matter be- 

 comes subject to a solar repulsion, and is urged away by this 

 force with a high velocity, and to great distances from the sun. 

 and that this repulsion augments in intensity as the comet 

 approaches the sun.* Now if such an energetic force of repul- 

 sion emanates from the sun, and operates on cometic matter at 

 all distances, both small and great, according to the law of in- 

 verse squares, there is assuredly a high probability that it may 

 play an important part on that vast arena, where solar forces 

 are obviously engaged in fierce contention. It maybe con- 

 jecture^ that the solar vapors are entirely difierent substances 

 from, and wholly unlike, in their physical state, the com- 

 etary vapors that appear to be so exceedingly subtil. Bnt it 

 IS certainly more philosophical to suppose that the same sul)- 

 stances, or substances possessed of the same general properties, 

 are present in all cosmical bodies, and the earth. Besides we 

 are not_ without direct evidence on this point. Huggins, by 

 examining the spectrum furnished by the Kght emitted from 

 the Comet II, 1868, detected the presence of the vapor of car- 

 bon in the brighter portions of the comet. " He has been able 

 to discriminate between the light of the nucleus of a comet and 

 that of its tail. The nucleus is self-luminous, and its substance 

 is in the form of ignited gas. The coma shines by reflected 

 light as clouds do." 



II, as IS now conceded by £ 

 made up of matter detached from the general mass of the comet. 

 l)y reason of a repulsive action exerted by the sun, it must ab<> 

 ')e admitted that the matter expelled is not all urged away l\v 

 the >ame intensity of force, and with the same velocity ; for we 

 Mnd that it is much more widely dispersed in the plane of tli^^ 

 <'onietary orbit than is consistent with this supposition. For 

 example, I have shown, in my theoretical discussion of Donati s 

 Coniet,t that if we conceive "particles of matter to have been 

 oxjielled from this comet, with a certain small lateral velocity, 

 and urged away during a certain interval of time by a solar 

 r3i)ulsion bearing to the force of gravitation the ratio ot 

 -ersally, admitted by a 



Journal, to establish by rigorous caicu- 



1 of Donati's comet was developed by a force ot sow 



ion— both varying accoraiut. 



