150 



Mr. J. N. Lockyer. 



[Nov. 17, 



Velocity 1 mile per second 3,000° C. 



„ 10. „ „ 300,000 



„ 20 „ „ 1,200,000 



„ 30 „ „ 2,700,000 



„ 60 „ „ 10,800,000 



It is clear, however, that we should under the conditions stated be 

 more frequently dealing with grazes than collisions. 



Comets due to Collisions of Meteorites. 



The fact that comets are due to swarms of meteorites was first 

 established by Schiaparelli in 1866, when he demonstrated that the 

 orbit of the August meteors was identical with that of the bright 

 comet of 1862* 



Nebulm due to Collisions of Meteorites. 



So far as I know the first suggestion that nebulae were really in 

 some manner associated with meteorites and not with masses of gas 

 was made by Professor Tait in 1871. f T have used the suggestion in 

 my lectures ever since, and it is now some years ago since I put it to 

 an experimental test by showing that both the spectra of comets and 

 nebula3, so far as carbon and hydrogen were concerned, could be pro- 

 duced from a vessel containing the vapours produced by meteorites. 

 More recently, M. Faye has stated in his works on the nebular hypo- 

 thesis that the solar nebula may as probably have consisted of a cloud 

 of stones as of a mass of gas. This view, however, has not been 

 favoured by Dr. Huggins, who in his observations both on nebulae and 

 comets has inferred from the near coincidence of the line of 500 with 

 the strong air line that we are probably in presence of nitrogen, or of 

 a form of matter more elementary than nitrogen ; the line at 373 being 

 attributed by him also to some unknown form of hydrogen on account 

 of its coincidence with one of the series of hydrogen lines in the ultra- 

 violet observed in the spectra of stars of the first class. 



"New Stars " due to Collisions of Meteorites. 



The idea that the Novas which appear from time to time are due to 

 collisions of meteorites was, I think, first advanced by myself in 1877, 

 when I wrote in connection with Nova Cygni : — 



* Letters to Father Secchi, printed in the ' Bollettino ' of the Collegio Komano, 

 and reproduced in • Les Mondes,' vol. 13. 



f " It seems to me that we have a series of indications of what (for want of a 

 better phrase) may be called the period of life of a star or group ; beginning with 

 the glowing gases developed by impacts of agglomerating cold masses. (Planetary 

 nebulae and others irresolvable, such as those of Orion, Lyra, &c, where the 

 spectrum consists of a very few bright lines only.)" (Professor Tait, 'Edinburgh, 

 Eoy. Soc. Proc.,' 1871.) 



