36 



NA rURE 



[XoVEMliER lO, 1896 



demonstrates the truth of the suggestion, made many 

 years ago by Prof. Tait before any spectroscopic facts 

 were available, that the nebulae are masses of meteorites 

 rendered hot by colhsions. 



Surely human knowledge is all the richer for this in- 

 dication of the connection between the nebulae, hitherto 

 the most mysterious bodies in the skies, and the " stones 

 that fall from heaven." 



Celestial evolution. 



But this is, after all, only a stepping-stone, important 

 though it be. It leads us to a vast generalisation. If 

 the nebulae are thus composed, they are bound to con- 

 dense to centres however vast their initial proportions, 

 however irregular the first distribution of the cosmic 

 clouds which compose them ; eacli pair of meteorites in 

 collision puts us in mental possession of what the final 

 stage must be. We begin with a feeble absorption of 

 metallic vapours round each meteorite in collision ; the 

 space between the meteorites is filled with the permanent 

 gases driven out further afield and having no power to 

 condense. Hence dark metallic and bright gas lines. 

 As time goes on, the former must predominate, for the 

 whole swarm of meteorites will then form a gaseous 

 sphere with a strongly heated centre, the light of which 

 will be absorbed by the e.\terior vapour. 



The temperature-order of the group of stars with 

 bright lines as well as dark ones in their spectra, has 

 been traced, and typical stars mdicating the chemical 

 changes have been as carefully studied as those in which 

 absorption phenomena are visible alone, so that now 

 there are no breaks in the line connecting the nebulae 

 with the stars on the verge of extinction. 



Here we are brought to another tremendous outcome, 

 that of the evolution of all cosmical bodies from meteor- 

 ites, the various stages recorded by the spectra being 

 brought about by the various conditions which follow 

 from the conditions. 



These are shortly that at first collisions produce 

 luminosity among the colliding particles of the swarm, 

 and the permanent gases are given oft' and fill the inter- 

 spaces. As condensation goes on, the temperature at 

 the centre of condensation always increasing, all the 

 meteorites in time are driven into a state of gas. The 

 ineteoritic bombardment practically now ceases for lack 

 ■of material, and the future history of the mass of gas is 

 that of a cooling body, the violent motions in the atmo- 

 sphere while condensation was going on now being 

 replaced by a relative calm. 



The absorption phenomena in stellar spectra are not 

 identical at the same mean temperature on the ascending 

 and descending sides of the curve, on account of the 

 tremendous difference in the physical conditions. 



In a condensing swarm, the centre of which is under- 

 going meteoritic bombardment from all sides, there cannot 

 be the equivalent of the solar chromosphere ; the whole 

 mass is made up of heterogeneous vapour at different 

 temperatures, and moving with different velocities in 

 different regions. 



In a condensed swarm, of which we can take the sun 

 as a type, all action produced from without has practically 

 ceased ; we get relatively a quiet atmosphere and an 

 orderly assortment of the vapours from top to bottom, 

 disturbed only by the fall of condensed metallic vapours. 

 But still, on the view that the differences in the spectra 

 of the heavenly bodies chiefly represent differences in 

 degree of condensation and temperature, there can be, 

 au fond, no great chemical difl'erence between bodies of 

 increasing and bodies of decreasing temperature. Hence, 

 we find at equal mean temperatures on opposite sides of 

 the temperature curve, this chemical similarity of the 

 absorbing vapours proved by many points of resemblance 

 in the spectra, especially the identical behaviour of the 

 enhanced metallic and cleveite lines. 



NO. 15 15, VOL. 59] 



Celestial dissociation. 



The time you were good enough to put at my disposal 

 is now exhausted, but I cannot conclude without stating 

 that I have not yet exhausted all the conceptions of a 

 high order to which Fraunhofer's apparently useless 

 observation has led us. 



The work which to my mind has demonstrated the 1 

 evolution of the cosmos as we know it from swarms ofi | 

 meteorites, has also suggested a chemical evolution^ | 

 equally majestic in its simplicity. 



A quarter of a century ago I pointed out that all the 

 facts then available suggested the hypothesis that in the 

 atmospheres of the sun and stars various degrees of 

 "celestial dissociation " were at work, la "dissociation" 

 which prevented the coming together of the finest par- 

 ticles of matter which at the temperature of the earth and 

 at all artificial temperatures yet attained here compose 

 the metals, the metalloids and compounds. 



On this hypothesis the so-called atoms of the chemist 

 represent not the origins of things, but only early stages 

 of the evolutionary process. 



At the present time we have tens of thousands of 

 facts which were not available twenty-five years ago. 

 All these go to the support of the hypothesis, and among 

 them I must indicate the results obtained at the last J 

 eclipse, dealing with the atmosphere of the sun in relation! 

 to that of the various stars of higher temperature toj 

 which I called your attention. In this way we can easily^) 

 explain the enhanced lines of iron existing practically' 

 alone in Alpha Cygni. I have yet to learn any other 

 explanation. 



I have nothing to take back either from what I then 

 said or what I have said since on this subject, and 

 although the view is not yet accepted, I am glad to know 

 that many other lines of work which are now being 

 prosecuted tend to favour it. 



I have no hesitation in expressing my conviction that 

 in a not distant future the inorganic evolution to which 

 we have been finally led by following up Fraunhofer's 

 useless expermient, will take its natural place side by 

 side with that organic evolution the demonstration of 

 which has been one of the glories of the nineteenth 

 century. 



And finally now comes the moral of my address. If I 

 have helped to show that observations ha\ing no imme- 

 diate practical bearing may yet help on the thought of 

 mankind, and that this is a thing worth the doing, let 

 me express a hope that such work shall find no small 

 place in the future University of Birmingham. 



DIFFUSION IN RELATION TO WORK. 



IN this month's Philosophical Magazine Mr. A. Grififiths 

 has an interesting paper on diffusion convection, in 

 which he suggests an indirect method of measuring rates 

 of diffusion of liquids, and concludes with the following 

 deduction from the fact that diffusion sometimes produces 

 convection currents and sometimes does not : — " Does not 

 this indicate that the heat produced on mixing a solution 

 with water depends on how the mixing takes place ? Is the 

 matter connected w ith a sort of surface-tension existing 

 in the spaces betw een a strong and a we.ak solution ? " 



Mr. Grifiiths docs not seem to have observed that his 

 investigation applies quite well to gases as to liquids, 

 and that his indirect method of measuring rates of diftusion 

 is applicable to gases. In the case of gases there can be 

 sensible surface-tension, and, as the theory of diffusion in 

 gases is quite simple, there is no serious dilTiculty in see- 

 ing how there is a dift'erence between different ways of 

 mixing them. 



It is generally known that two different gases may be 

 mixed by irreversible, or by, at least, partially reversible, 



