NATURAL PHILOSOPHY. 119 



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 decreasing or going 

 through regular periods of varied lengths, and many degrees of grada- 

 tion in brightness. The same may also be inferred from the geologi- 

 cal discoveries, of there having 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 

 much 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. 



In this connection some theoretical views have recently been pre- 

 sented to the Royal Astronomical Society, by Mr. James Nasmyth, 

 from which we make the following extracts : 



" A course of observations on the solar spots, and on the remarkable 

 features which from time to time appear on the sun's surface, which I 

 have examined with considerable assiduity for several years, had in the 

 first place led me to entertain the following conclusions, namely, that 

 whatever be the nature of solar light, its main source appears to result 

 from an action induced on the exterior surface of the solar sphere, a 

 conclusion in which, I doubt not, all who have attentively pursued 

 observations on the structure of the sun's surface will agree. Im- 

 pressed with the correctness of this conclusion, I was led to consider 

 whether we might not reasonably consider the true source of the la- 

 tent 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 through- 

 out the boundless regions of space, and which in that case must be per- 

 fectly 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 dif- 

 fused 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 brotherhood, in some portions of his vast stellar orbit, 

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

 which this element may either abound or be deficient, and so cause 

 him to beam forth with increased splendor, or fade in brilliancy, just 

 in proportion as the richness or poverty of this supposed element may 

 occur in those regions of space through which our sun, in common 

 with every stellar orb, has passed, 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 brightness of 

 stars, and more especially of those which have been known to beam 

 forth with such extraordinary splendor, and have again so mysteriously 

 faded away. 



Finally, in reference to such a state of change having come over 



a 



