1.887.] 



Researches on the Spectra of Meteorites, 



lol 



" The very rapid reduction of light in the case of the new star in 

 Cygnus was so striking that I at once wrote to Mr. Hind to ask if 

 any change of place was observable, because it seenied obvious that, 

 if the body which thus put on so suddenly the chromospheric spectrum 

 were single, it might only weigh a few tons, or even hundredweights, 

 and, being so small, might be very near us. Mr. Hind's telescope was 

 dismounted, and I have not yet got any information as to the change 

 of position ; and as I am now writing in the Highlands, away from 

 all books, I have no opportunity of comparing the position now given 

 by Lord Lindsay in R.A. 21h." 36m. 52s., Deck + 42° 16' 53", with 

 those given on its first appearance by Winnecke and others. 



" We seem driven, then, from the idea that these phenomena are 

 produced by the incandescence of large masses of matter, because if 

 they were so produced, the running down of brilliancy would be 

 exceeding slow. 



" Let us consider the case, then, on the supposition of small masses 

 of matter. Where are we to find them ? The answer is easy : — in 

 those small meteoric masses which, an ever-increasing mass of evi- 

 dence tends to show, occupy all the realms of space."* 



The Effects of Collisions. 



The question of what must happen to the meteorites themselves in 

 consequence of this system of collisions is worth going into thoroughly. 

 A very cursory examination seems to indicate that much light is 

 thrown on the condition of meteorites as we know them, and their 

 division into iron and stony. 



As 30 miles per second is a very frequent value obtained for the 

 velocity of meteorites when they enter our atmosphere, it is possible 

 to compare temperatures brought about by collisions with those pro- 

 duced by passage through our atmosphere. Two masses of meteoric 

 iron meeting each other in space would probably, if moving with a 

 certain velocity, be formed into a pasty conjoined mass, and this 

 process might go on until an iron of large dimensions was formed, 

 and the various meteorites thus welded together would present in time 

 a very fragmentary appearance. While irons were thus increasing in 

 size, collisions with smaller meteorites would be attended with very 

 local increases of temperature, perhaps sufficient to volatilise the 

 surface or allow it to be indented, and in this manner the well-known 

 ''thumb-marks" receive explanation. 



The masses of iron, when in a state of fusion, whatever their size, 

 would be able to include stony meteorites in their vicinity. In the 

 case of stones it is easy to see that the result would be very different. 

 Their collisions would have, most probably, the effect of reducing 

 large pre-existing masses to smaller ones, and the collision of a large 



* 1 Nature,' toI. 16, p. 413. 

 VOL. XLIIT. M 



