Theories of Crystallography. 159 



preparation, it forms a very brilliant glazing, which, in the 

 course of two days in summer, acquires all the solidity that 

 may be required. 



The same essence employed with copal of two fusions, 

 that is to say, copal liquefied a second time, takes up a third 

 more than in the former case. But it produces very little 

 effect on copal not prepared. 



The facility which attends the preparation of thi3 varnish 

 by the new method here indicated, will admit of its being 

 applied to all coloured grounds which require solidity, 

 pure whites alone excepted. Painted boxes, therefore, and 

 all small articles, coloured or not coloured, where it is 

 required to make the veins appear in all the richness of their 

 tones, call for the application of this varnish, which pro- 

 duces the most beautiful effect, and which is more durable 

 than turpentine varnishes composed with other resinous 

 substances. 



XXIX. Parallel of Rome de L'Isle^s and the Abbi 

 Haly's Theories of Crystallography. 



To Mr. TillocL 

 DEAR sir, 



too early as in the first number of the Philosophical Maga- 

 zine you turned your attention to the Abbe HauVs theory 

 of crystallography : you seemed to predict that his labours 

 might lead on some future day to deep philosophical re- 

 search. An erroneous opinion, however, has been pretty 

 generally propagated in this country as to the similarity of 

 the systems of Rome de ITsle and of the Abbe Haiiy, which 

 gave rise to the enclosed paper. With leave of the author, 

 the Abbe Buee, who had written it in French for a friend 

 pf his, I send you a translation of it. It may awaken the 

 energies of the learned public ; and it may be gratifying; to 

 you to find that the science of crystallography, as treated 

 by the Abbe Haiiy, will probably lead to the most philoso- 

 phical results. May I, therefore, request the insertion of 

 }t in one of your ensuing numbers ? 



I remain, sir, yours, &c. 

 Welbeck-street, No. 10. JR. CLIFFORD 



A Utter 



