244 



SCIEiMCE. 



[Vol. XIX. No. 482 



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THE DETECTION OP ARTIFICIAL (IMITATION) 

 GEMS. 



In most works on gems much stress is laid upon " hard- 

 ness " as a means of distinguishing real from artificial 

 " stones." Having had occasion during the past two years 

 to examine several emeralds, rubies, etc., as to their gen- 

 uineness, I have come to the conclusion that this property — 

 which is, as everyone knows, of great assistance in the de- 

 termination of uncut minerals — is of very little value in the 

 examination of cut and polished gems, inasmuch as cutting 

 a stone renders its surface much softer — in some cases re- 

 ducing the hardness by over one-tenth — so that it can be 

 "scratched" by minerals considerably lower in the scale of 

 hardness than itself in its natural condition. On the other 

 hand, many artificial gems will scratch ordinary window- 

 glass quite readily, and have a hardness nearly equal to that 

 of quartz, although it is popularly believed that if a " dia- 

 mond " scratch glass it must be real. 



Polishing the surface of a stone also necessarily affects its 

 specific gravity, especially if the specimen be of small size, 

 as is the case with most gems. Specific gravity as a means 

 of detecting false gems is also rendered practically valueless 

 by reason of the fact that special care is often taken in the 

 manufacture of these articles to make them have specific 

 gravities as nearly like the natural species which they are in- 

 tended to imitate as possible. 



Gems being usually much facetted, an examination of their 

 optical properties becomes difiicult and is of very little use 

 in their practical determination. 



Many gems are thought by their owners to be genuine on 

 account of their having been in the possession of themselves 

 or families as heirlooms for many years. Age in this case 

 is no criterion as to value, as it is well known that the 

 ancient Egyptians and Greeks were well versed in the man- 

 ufacture of artificial stones. 



The grand and really only reliable test, it seems to me, as 

 to the genuineness or otherwise of a gem — in case we do 

 not wish to totally destroy the specimen — is an examination 

 of its fusibility. Artificial diamonds, emeralds, etc., if held 

 in the border of the flame of a spirit-lamp or Bunsen burner 

 soon become rounded on their edges, their fusibilities being 

 generally considerably under three, according to von Kobell's 

 scale of the fusibilities of minerals. The real stones, dia- 

 monds, etc., with the exception of the garnet, are practically 

 infusible. 



Great care should be taken in the examination of the fusi- 

 bility of a gem, as, if the latter be genuine, it may, unless 

 heated gradually and carefully, crack and fly to pieces on 

 exposure to a high temperature. Moreover, some gems will 

 change color if heated too highly. W. G. Miller. 



University of Toronto. 



THE SYSTEMATIC POSITION OF THE DIPTEEA. 



Having been a student of the Diptera for two years, I have 

 come to the conclusion that the order is entitled to the dis- 

 tinction of being, as a whole, more highly specialized than 

 any other. Entomologists who have attempted a general 

 classification of insects have almost uniformly regarded the 

 Hymenoptera as the highest order, placing the Lepidoptera 

 second, and the Diptera third. The only exception in Amer- 

 ica, I believe, is Professor Hyatt, who, in a recent book 

 ("Insecta," by Alpheus Hyatt and J. N. Arms), has placed 

 the Diptera at the head of the class, with the Hymenoptera 

 second, and the Lepidoptera third. His argument for this 

 arrangement is brief and forcible. The main features may 

 be summarized as follows: — 



The essential question which settles the rank of any insect 

 is, How far does it deviate in structure, and through what 

 line of descent has it developed, from its Thysanuriform an- 

 cestors ? To introduce the subject of instinct or of useful- 

 ness to man is to confuse our ideas, for we cannot translate 

 the data furnished by such a criterion into terms of the other 

 standard. Applying this principle, he takes the following 

 features of Diptera to show that they possess a degree of 

 specialization surpassing any other order: — 



1. Larval structure: '"The young of even the generalized 

 forms of Diptera are, as a whole, farther removed from the 

 Thysanuriform type than those of any other group. The 

 secondary larval form, which in the case of the Diptera is 

 always footless and often an almost headless maggot, has 

 complete possession of the younger stages. As Friedrich 

 Brauer has pointed out, the general absence in the larvae of 

 Diptera of the thoracic legs, even although living in situa- 

 tions that seem to demand their development, shows that 

 they must have inherited this peculiarity from an ancestral 

 form whose larva had lost them. This comparative infiexi- 

 bility of the larval stage is sufiicient of itself to show that 

 there is now a wide gap between the existing Diptera and all 

 other orders of insects, and that this chasm is not closed by 

 the resemblances of the parts in the adult to those of the 

 Lepidoptera or isolated forms in other orders" (pp. 273, 274j. 



2. The presence of but two wings: "The tendency to the 

 enlargement of one pair of wings, like the tendency to the 

 enlargement of certain pairs of thoracic legs and the reduc- 

 tion of other pairs, or a change in their structure and func- 

 tion, so that the insect makes a departure from the conven- 

 tional normal type of four equal membranous wings and six 

 equal-jointed legs, is everywhere an index of specialization " 

 (p. 274). 



