160 Mr. J. N. Lockyer. On the Classification [Jan. 10, 



I. "ON THE SPECTRA OF METEORIC SWARMS IN THE 

 SOLAR SYSTEM." 



I. VIEWS OF REICHENBACH, SCHIAPARELLI, AND TAIT. 



Reichenbach was the first to bring forward a large amount of 

 evidence (founded on the study of meteorites) indicating that comets 

 were in all probability swarms of meteorites* in our own system 

 moving in orbits round the sun. 



Accepting as proved by the then knowledge the most intimate 

 connexion between meteorites and falling stars, Reichenbach reasoned 

 that both were connected with comets in the following manner. He 

 first recapitulated the facts then accepted with regard to comets : 



(1.) Comets, both tail and nucleus are transparent. 



(2.) Light is transmitted through comets without refraction ; hence 

 the cometary substance can be neither gaseous nor liquid. 



(3.) The light is polarised, and therefore borrowed from the sun. 



(4.) Comets have no phases like those of moon and planets. 



(5.) They exercise no perturbing influences. 



(6.) Donati's comet (which was then visible) in its details and its 

 contour is changing every day according to Piazzi, almost hourly. 



(7.) The density of a comet is extremely small. 



(8.) The absolute weight is sometimes small (von Littrow having 

 calculated the masses of very small comets, tail and all, as scarcely 

 reaching 8 Ibs ). 



From these data the following conclusions might be drawn : 



(1.) That a comet's tail must consist of a swarm of extremely small 

 but solid particles, therefore granules. 



(2.) That every granule is far away from its neighbour in fact, 

 so far that a ray of light may have an uninterrupted course through 

 the swarm. 



(3.) That these granules, suspended in space, move freely and yield 

 to outer and inner agencies agglomerate, condense, or expand ; that 

 a comet's nucleus, where one is present, is nothing else than such an 

 agglomeration of loose substances consisting of particles. 



Hence we must picture a comet as a loose, transparent, illuminated, 

 free-moving swarm of small solid granules suspended in empty space. 



The next step in Reichenbach's reasoning was to show that 

 meteorites (of which he had a profound knowledge) were really 

 composed of granules. 



He pointed out that these granules (since called chondroi) formed 

 really the characteristic structure both of irons and stones, so that both 

 orders were chiefly aggregates of chondroi stony ones in iron 

 meteorites, iron ones in stony meteorites. 



* Poggendorff, ' ^Tinalen,' vol. 105, 1858, p. 438. 



