1823.] Mr, Brooke^s Introduction to Crystalhgrajphy, 143 



greater proportion than one strictly arithmetical ; because, while 

 by the combustion of denser gases a higher temperature is pro- 

 duced, the coohng agencies remain the same. It is probable, 

 therefore, that of two gases, composed of the same ingredients, 

 that which has a double density will afford somewhat more than 

 a double quantity of light." — Edit, 



2. A Familiar Introduction to Crystallography ; including an 

 Explanation of the Principle and Use of the Goniometer, 

 With an Appendix, containing the Mathematical Relatione of 

 Crystals, Rules for drawing their Figures; and an Alphabetical 

 Arrangement of Minerals, their Synonymes, and Primary 

 Forms. Illustrated by nearly 400 Engravings on Wood, By 

 Henry James Brooke, FRS. FLS. &c. London, 1823. 



Nearly a quarter of a century has now elapsed, since the late 

 Abbe Haliy first presented science, in a complete and systematic 

 form, in his Traite de Mineralogie, with the results of the beau- 

 tiful investigations of the geometric characters and structure of 

 mineral substances, in which he had then for some years been 

 engaged ; and many of which he had published before in 

 detached memoirs, inserted in the Journal des Mines, and other 

 periodical works. Attempts had been made by various writers 

 on mineralogy early in the last century, to confer a scientific 

 form on the knowledge of crystaUized bodies, but it is to Rome 

 de L'isle that we are indebted for the first definite rudiments of 

 crystallography, and likewise for the first useful application of 

 the science to the determination of mineral species. The struc- 

 ture of crystals, however, appears to have been first noticed by 

 Bergman, and Gahn, and also, about the same time, by our inge- 

 nious countryman, Mr. Keir, of Birmingham. All the subjects 

 which had attracted the attention of these observers were pur- 

 sued with astonishing industry and success by Haiiy, who, by a 

 precise determination of the different crystalline forms belonging 

 to a considerable number of minerals, and by various philoso- 

 phic general views founded upon that determination, completed 

 the establishment of mineralogy upon a truly scientific basis ; to 

 which the great improvements and discoveries in the chemical 

 analysis of minerals on the one hand, and the minute examina- 

 tion of their external characters instituted by Werner on the 

 other, had already very efficiently contributed. 



Since the first publication of Haiiy's treatise, however, little 

 progress has been made in crystallographic science, particularly 

 in this country, while almost every other branch of natural phi- 

 losophy has received the most important accessions during that 

 period. Even at the present time, this science, comparatively 

 speaking, has but few votaries among us, and many persons to 

 whose pursuits a thorough acquaintance with it would seem to be 



