182 Professor C. Piazzi Smyth's Meteorological 



portant question can only be attempted by the naked eye, 

 and of one who has been practised in observing the zodiacal 

 light ; but, even then, may perhaps require a rarer and 

 clearer atmosphere than any of the small hill tops in any fea- 

 sible part of the direction of the line of eclipse may attain to. 

 Of the Nature and Source of the Sun's Light and Heat. — 

 That so brilliant a display is kept up by the combustion or 

 destruction of something, appears to be generally if not uni- 

 versally maintained, but v^hat that matter may be, and how 

 supplied, no probable guess has yet been made. The intensity 

 of the solar light and heat is easily proved, and that it re- 

 sides chiefiy, if not entirely, at the surface ; and that surface 

 on being closely watched, is found to be in a state of excessive 

 agitation, and experiences periodical disturbances and altera- 

 tions-of a very excessive character. When periodical changes 

 are seen, we may expect secular ones also ; and if the 

 former were of a regular character the latter might be 

 necessarily inferred, but although no regular law has yet 

 been made out for the sun, the probability of their slow 

 variations through long periods of time is great, and is 

 increased when we turn our attention to those other suns, 

 the stars, and find some of them increasing and others de- 

 creasing, or going through regular periods of varied lengths, 

 and many degrees of gradation in brightness. The same may 

 also be inferred from the geological discoveries, of their hav- 

 ing been formerly glacial ages in the world, and again torrid 

 ones, for there is no other cause that we know of equal to 

 produce the effects observed ; while, if our sun were to have 

 increased or decreased in the amount of light and heat 

 thrown out, as mu€h as some stars have done during the 

 last four years, all organic bodies might have perished on 

 the surface of the earth before now from excess, or from lack 

 of heat. 



The question is, therefore, one well worthy of being in- 

 quired into instrumentally, and it is to be hoped that it will be 

 taken up in a business manner by some one before long. In 

 the meanwhile, anything tending to explain the real nature 

 of the phenomena may be of use, as serving to render the di- 

 rection of observations more certain, and as some novel views 



