328 Prof. J. N. Lockyer. On the Photographic [Dec. 8, 



suggested the hypothesis that all celestial bodies are, or have been, 

 swarms of meteorites, the difference between them being due to 

 different stages of condensation. The new classification rendered 

 necessary by this hypothesis differed from previous ones, inasmuch as 

 the line of evolution followed, instead of locating the highest tem- 

 perature at its commencement, as demanded by Laplace's hypothesis, 

 placed it much later. Hence bodies of increasing temperature were 

 demanded as well as bodies of decreasing temperature. 



The question how far this condition is satisfied by the new facts 

 revealed by the photographs is next discussed. 



This involves the consideration of some points in connexion with 

 the hypothesis to which brief reference alone has been made in pre- 

 vious communications. The phenomena to be expected on the 

 hypothesis, and the actual facts, are given side by side below. 



Nebulce. 



The br'ght lines seen in nebulas 

 should have three origins : 



(1.) The lines of those sub- 

 stances which occupy the inter- 

 spaces between the meteorites. 

 Chief among these, from labora- 

 tory experiments, we should 

 expect hydrogen and gaseous 

 compounds of carbon. 



(2.) The most numerous colli- 

 sions between the meteorites will 

 be partial ones mere grazes 

 sufficient only to produce com- 

 paratively slight rises of tempera- 

 ture. 



(3.) There will, no doubt, be a 

 small number of end-on collisions, 

 producing very high temperatures, 

 and there should be evidence of 

 some high-temperature lines. 



'(1.) Lines at wave-lengths ap- 

 proximately very closely to the 

 lines of hydrogen, and to some 

 of the carbon flutings, appear in 

 the spectra of nebulae. 



(2.) There is a fluting most 

 probably due to magnesium at 

 X 500, and the longest flame lines 

 of iron, calcium, and magnesium 

 are seen. 



(3.) The chrornospheric line 

 D 3 and another line at X 4471 

 (which is always associated with 

 D 3 in the chromosphere) have 

 been recorded in the spectrum of 

 the Orion Nebula. 



Bright-Line Stars. 



The lines seen in the spectra of 

 bright-line stars should, in the 

 main, resemble those which ap- 

 pear in nebulae. They will differ, 

 however, for two reasons given 

 in the paper. 



Professor Pickering has shown 

 that the Draper Memorial photo- 

 graphs prove that bright-line stars 

 are intimately connected with the 

 planetary nebulae, the lines in the 

 spectra being almost identical. 



