l64 Professor C. Piazzi Smyth's Meteorological 



led to consider whether we might not reasonably consider 

 the true source of the latent element of light to reside, not in 

 the solar orb^ but in space itself ; and that the grand function 

 and duty of the sun was to act as an agent for the bringing 

 forth into vivid existence its due portion of the illuminating 

 or luciferous element, which element I suppose to be diffused 

 throughout the boundless regions of space, and which in that 

 case must be perfectly exhaustless. 



*' Assuming, therefore, that the sun's light is the result 

 of some peculiar action by which it brings forth into visible 

 existence the element of light, which I conceive to be latent 

 in, and diffused throughout, space, we have but to imagine 

 the existence of a very probable condition, namely, the unequal 

 diffusion of this light-yielding element, to catch a glimpse of 

 a reason why our sun may, in common with his solar brother- 

 hood, in some portions of his vast stellar orbit, have passed, 

 and may yet have to pass, through regions of space, in which 

 the light-yielding element may either abound or be deficient, 

 and so cause him to beam forth with increased splendour, or 

 fade in brilliancy, just in proportion to the richness or poverty 

 of this supposed light-yielding element as may occur in those 

 regions of space through which our sun, in common with every 

 stellar orb, has passed, is now passing, or is destined to pass, 

 in following up their mighty orbits. 



" Once admit that this light-yielding element resides in 

 space, and that it is not equally diffused, we may then catch 

 a glimpse of the cause of the variable and transitory bright- 

 ness of stars, and more especially of those which have been 

 known to beam forth with such extraordinary splendour, and 

 have again so mysteriously faded away ; many instances of 

 which abound in historical record. 



" Finally, in reference to such a state of change having 

 come over our sun, as indicated by the existence of a glacial 

 period, as is now placed beyond doubt by geological research, 

 it appears to me no very wild stretch of analogy to suppose 

 that in such former periods of the earth's history our sun 

 may have passed through portions of his stellar orbit in which 

 the light-yielding element was deficient, and in which case 

 his brilliancy would have suffered the while, and an arctic 



