1892.] Mineralogy and Petrography. 428 



his enterprise in the preparation of this, the only modern classification 



of massive rocks published. Instruments.— Salomon' describes a 



simple piece of apparatus by means of which the density of a heavy 

 liquid may be rapidly determined without the inconvenience of the use 



uated tube, win-. ■ manipulation depends upon tlio principle that tin- 

 heights of the liquid columns in its two anus will van with their dif- 

 ferences in density. By the aid of the instrument the specific gravity 

 of each mineral in a rock powder maybe determined without once 



emptying it of its solution. Four new microscopes for crvstallo- 



graphic and petrographical purposes have lately been introduced to 

 the favor of investigators. The three 2 from the manufactory of Zeiss 

 in Jena present no peculiar features. The fourth was made by Naehci 

 to the order of Wyrouboff 3 , especially for observations at high tem- 

 peratures. The objective is below the object, and the nicol prism and 

 the illuminating mirror are above it. The stage is fixed, while the 

 microscope body revolves. Attempts to use converged light with this 

 instrument have failed, because of the great heat to which the conden- 

 sers are subjected. 



'Neues. Jahrb. f. Min., etc., 1891, ii, p. 214. 



2 Czapski, Neues. Jahrb. f. Min., etc., B B. vii, p. 497. 



:i Bull. Soc. Franc' a. Min. xiv.. 1S91, p. 198. 



