1870. J Notices of Scientific Works. 81 



Each volume is accompanied with a beautiful coloured plate as 

 a frontispiece, and numerous well-executed lithographs. It suffices 

 to say that the whole work is produced in Mr. Van Voorst's best 

 style, and will form a valuable addition to his well-known trea- 

 tises of reference on Natural History. 



SCHKAUFS HANDBOOK OF PBECIOUS STONES. 



To any one who is not familiar with the elements of mineralogy, a 

 cabinet of precious stones— however rich and rare — has no more 

 educational value than a collection of shells can have to a person 

 ignorant of the anatomy of the mollusca. Yet it is by no means 

 needful to plunge into the depths of mineralogic lore in order to 

 appreciate the scientific value of a gem. All that is necessary is a 

 moderate acquaintance with the physical and chemical characters of 

 the comparatively few minerals which rank as precious stones, and 

 of those substances which are likely to be mistaken for genuine 

 gems. Dr. Schrauf, of Yienna, has recently published a text- 

 book,* which gives, within a moderate compass, all that mineralo- 

 gical information which the collector ought to have at hand. 



The early chapters of the work are devoted to a discussion of 

 mineralogical physics — a subject which no one can handle better 

 than the author of the elaborate Lehrbuch der physikalischen 

 Mineralogie. 



Popularly, yet accurately, he tells us all that we need know on 

 the crystalline form of minerals, their hardness, density, thermal, 

 electric, magnetic, and optical properties. Then follows a chapter 

 on the forms in which precious stones are commonly cut by the 

 jeweller. Each gem is then described separately, in order of value, 

 commencing, of course, with the diamond. 



In the chapter on Diamond, our author proposes a new formula 

 for determining the value of this stone — a formula which is said to 

 give results coinciding with the present market value of diamonds, 

 and is, moreover, applicable to stones of high weight. Let a 

 denote the current price of one carat ; then the value of a diamond 

 weighing m carats will be, according to Schrauf's formula, 



m 



2 (m + 2) a. 



To illustrate the application of this rule, we may calculate the 

 value of . the celebrated Sancy diamond, which was sold only a year 

 or two ago, and to which so romantic a history is attached. This 



* 'Handbuch der Edelstemkvmde,' von Dr. Albrecht Schrauf. Wien, ]869. 

 Pp. 252. 



VOL. VII. G 



