1887.] Researches on the Spectra of Meteorites. 155 



spectrum of carbon in the case of comets. Sudden changes from one 

 spectrum to the other are seen in the glow of meteorites in vacuum 

 tubes when a current is passing, and the change from H to C can 

 always be brought about by increased heating of the meteorite. 



XIV. Meteorites are formed by the condensation of vapours thrown 

 off by collisions. The small particles increase by fusion brought 

 about again by collisions, and this increase may go on until the 

 meteorites may be large enough to be smashed by collisions, when the 

 heat of impact is not sufficient to produce volatilisation of the whole 

 mass. 



XV. Beginning with meteorites of average composition, the extreme 

 forms, iron and stony, would in time be produced as a result of colli- 

 sions. 



XVI. In recorded time there has been no such thing as a world on 

 fire, or the collision of masses of matter- as large as the earth, to say 

 nothing of masses as large as the sun ; but the known distribution of 

 meteorites throughout space indicates that such collisions form an 

 integral part of the economy of nature. The number of bodies, how- 

 ever, subject to such collisions is extremely small, and must, it would 

 appear, form but a small percentage of the celestial bodies, seeing 

 that they must be dark and cold. . 



XVII. Special Solar Applications. 



a.. The solar spectrum can be very fairly reproduced (in some parts 

 of the spectrum almost line for line) by taking a composite photo- 

 graph of the arc spectrum of several stony meteorites, chosen at 

 random, between iron meteoric poles. 



/3. The carbon which originally formed part of the swarm the con- 

 densation of which produced the solar system, has been dissociated 

 by the high temperature brought about by that condensation. 



7. The indications of carbon which I discovered in 1874 ('Roy. 

 Proc. Soc.,' vol. 37, p. 308) will go on increasing in intensity slowly, 

 until a stage is reached when, owing to the reduction of temperature 

 of the most effective absorbing layer, the chief absorption will be that 

 of carbon — a stage in which we now find the stars of Class III6 of 

 Vogel's classification. 



8. At the present time it seems probable that among the chief 

 changes going on in the solar spectrum are the widening of K and the 

 thinning of the hydrogen lines. 



I have finally to express my great obligations to Messrs. Fowler, 

 Taylor, and Richards, who have helped me in various ways in the 

 researches embodied in this paper. Mr. Fowler, the assistant to the 

 Solar Physics Committee, has made most of the observations on 

 meteorites, and low-temperature spectra generally, which have been 



