On the Origin of the Light of the Sun and Stars. 453 



Piazzi Smyth, when this is the case both components change 

 together and in the same direction. We may soon hope to 

 learn something more definite regarding these bodies, which 

 are favourite subjects of study, but in the meantime our know- 

 ledge is very limited. 



From all this it is evident that in the case of many stars we 

 cannot suppose the light to be due to an incandescent solid 

 or liquid body, otherwise how can we account for their long- 

 continued disappearance ? Groodricke indeed has supposed that 

 dark bodies may periodically obscure them, but the objection 

 to this hypothesis is, that such a dark body would be of a size 

 utterly disproportioned to that of any ordinary star. Nothing 

 appears so capable of explaining all these phenomena as the 

 supposition that the luminosity of stars is derived from without, 

 and that when the source of excitement fails or varies we have 

 a temporary or variable star. Driven, therefore, to look with- 

 out for the source of solar and stellar light, let us examine the 

 various hypotheses which have been proposed. 



It has been argued that the etherial medium which per- 

 vades space may somehow produce luminosity at the sur- 

 face of large bodies, towards which it may be supposed to 

 stream, and that some of its streams being stopped by 

 planets or other bodies, this may occasion a variation in 

 the light of the primary; yet how, on this principle, are 

 we to account for the total stoppage of light for a length- 

 ened period of time ? Again, it has been supposed that our 

 sun is fed by meteors, which, falling into his atmosphere, have 

 their motion at once converted into light and heat. Accord- 

 ingly, when a star is in a portion of space rich in meteors, its 

 brightness will be intense ; but when in a space devoid of 

 meteors, it will disappear. This will readily account for the 

 behaviour of temporary stars, but it cannot easily be tortured 

 into affording us an explanation of variable ones. In advanc- 

 ing our own views, let us remark that in a case like the pre- 

 sent we should endeavour to connect together such phenomena 

 as are periodical. Can these appearances, then, be in any way 

 due to planets ? And again, since observation only can decide 

 this question, have the spots on our own sun any relation 

 to planetary configurations ? In the valuable work on sun 

 spots, recently published by Mr. Carrington, a comparison is 

 instituted between the frequency of sun spots and the radius 

 vector of Jupiter, and on the whole there are good grounds for 

 supposing that the least distance of Jupiter from the sun cor- 

 responds in epoch to the minimum of spot-frequency, and his 

 greatest distance to its maximum. It may be added that in 

 1837 the number of spots was peculiarly great, and that both 

 Jupiter and Saturn were then nearly at their greatest distances 



