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expanse still further beyond. The parting with its heat implies a cooling, and 

 cooling implies contraction of the mass. It is no assumption to suppose that in 

 the then nebulous condition of the Solar System, we see the germs of that system 

 as now it is known to us. Rotation round an axis, however caus'jd, seems a 

 necessary condition of matter, when unaffected, or but distantly affected, by 

 matter external to itself. The great law of gravitation would cause masses 

 vinequally cooled, and by consequence more or less contracted, and therefore 

 more or less heavy in proportion to bulk, to gravitate towards the centre. 

 Hence, if from no other cause, would arise a swaying of the whole mass, and 

 in time a motion round the centre of gravity, the point of rest of the vast 

 congeries of atoms thus held together by cohesion. Rotation once commenced, a 

 centrifugal force would be generated. Such force would tend to throw off 

 portions of matter, which sudden cooling might nearly solidify ; and hence, we 

 may well suppose, were detached those separated particles of the original 

 solar mass, which we now recognise as the planetary attendants of the Sun. 

 The rings of Saturn seem an exceptional case, where a repetition of this process 

 of detachment stopped short of breaking up into smaller bodies, known to us, 

 in other cases, as the " satellites " of the primary planets. But there is an 

 old proverb that the " exception proves the rule ; " so, here, in this instance of 

 Saturn's rings, we can detect a cause in operation, the results of which, in all 

 other cases, have their visible expression in the " Moons," which accompany 

 80 many of the larger planets of our system. 



Of this vast process of life and development, heat would seem to be 

 the moving power. The functions of light, at this earliest period of creative 

 formation, it is less easy to detect. But, to come down from these earlier 

 ages of creation's life, to the present time, as we now behold the Sun, with his 

 circling planets around, light, as well as heat, becomes an agent all essential 

 to the existence, and to the operations, not only of the animal and vegetable 

 kingdoms, but even of the solid materials of the mass of the earth itself. 



To dwell at any length on heat and its agencies, in ages long past, as in the 

 "carboniferous era," or even in our own day, as to the variations of climates 

 and seasons, would extend these remarks too far. But it may be of interest to 

 touch upon, however slightly, the subject of the photosphere of the Sun, and 

 to lay before you the most recent discoveries in relation thereto. I prefer to 

 do this in the very words of the reports of the Royal Astronomical Society, 

 by giving you a condensed statement of facts, leaving the application of these 

 facts, and their bearing upon the special subject of study of our clab, to the 

 hearer. 



Before I quote the extracts alluded to, I would remark that the process of 

 discovery of the nature of the solar atmosphere was as follows : — The solar 

 spectrum, formed by the prism, had long been known to men of science. lu 

 1802, Dr. 'Wollaston was the first to observe some dark lines in this spectrum ; 

 vertical dark lines here and there, not separating the prismatic colours, but 

 apparently arranged without order. These dark lines were subsequently more 



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