l6o ROCHESTER ACADEMY OF SCIENCE. 



62 groups. A representation, so far as possible, of each one of these 

 groups is, for evident reasons, a desirable feature in any collection. 



N. B. — It is interesting to notice that all of Brezina's 42 groups 

 of aerolites contain at least one stone seen to fall. 



The same is also true of Meunier's 28 aerolite types. 



THE PROPORTION OF SPECIMENS OF GREAT RARITY USUALLY THE 



MASS SMALL AT THE OUTSET. 



This is a factor whose merit is evident. Rare specimens of 

 any natural object are ever valued. But there are still several 

 kinds of rarity, one higher than another in value. 



1. There are a very limited number of meteorites which are 

 represented by only a single specimen, and that a small one. The 

 chance of this specimen ever being cut into and distributed is very 

 small indeed. These are and will remain uniques. There are a few 

 — hardly more than a score — of these ; Paris, London and Vienna 

 have the greater part. In other instances the small original has 

 been divided into but three or four individuals, which have gone 

 into as many different collections, and will stay there undisturbed. 

 In spme cases the individual mass was large ; but it has been lost, 

 and there are but small fractions — and these, small pieces — existing 

 in collections. All the above are practically unattainable by other 

 than the favored collection possessing them, and then they confer 

 very especial merit on that collection. As a rule, only the very 

 largest public collections possess specimens of this category of merit. 



2. There is another kind of rarity less interesting to consider. 

 This is where there was a large mass at the outset — enough to sup- 

 ply all collections. But it has been the policy of the museum or 

 of the amateur collector into whose hand this mass came, to hoard 

 it, refusing its distribution. In this case the meteorite is artificially 

 rare, and the collection has attained an increased value by the 

 selfish course pursued. 



The proportion in any collection of meteorites possessing either 

 of these two classes of rarity gives that collection signal value. 

 The size and weight of such specimens is an important item in the 

 valuation. 



THE COMPLETENESS OF ORIGINAL EXTERIOR STRUCTURE, WITH CRUST, 

 PITTING, ORIENTATION, ETC. 



While nearly every meteorite — whether iron or stone — shows 

 itself clearly to be a fragment torn originally from a larger mass, 

 it is often of interest to have that mass just as it reached our earth, 



