l-iS'i Journal of Applied Microscopy 



about this axis is accompanied by a rotation of the dark brush in the opposite 

 directions, is shown in the same manner. Minor facts, such that one arm of the 

 cross is broader than the other, and that the hyperbola branches broaden the 

 further we go from optic axis, may also be shown. a. j. m. 



Schenck. R Ueber die Dynamik der Krystalle. starting with the proposition that, "with 

 Central blatt Min. Geol. Palaen. 313, 1900. _ r t- ' 



crystallized material the free physical 



and chemical energy is dependent on the direction," the writer assumes that all 

 equations involving vapor pressures are valid for solution pressures since there 

 is perfect analogy between these pressures. If, then, any crystal is considered 

 to be a volatile chemical substance with different crystal faces, and if all but two 

 of these faces are coated with a layer which hinders vaporization, then on these 

 two free faces there will be different pressures. If A possesses the higher pres- 

 sure and B the lower, then A yields vapor, or crystal molecules, until the surround- 

 ing medium is saturated therewith but the medium being supersaturated for B T, 

 the vapor, or crystal molecules, condense on B T. If the vapor pressure at both 

 faces is known, the work done in transporting one gram-molecule from one crystal 

 face to another can be calculated. A system of formula; are given which practi- 

 cally apply the principles of thermodynamics to crystallographic problems. As 

 a practical example, crystals of potash alum were coated with shellac, but on 

 some the octahedral faces were not covered, on some the cube faces, and on 

 some the dodecahedral faces. The velocity of weathering at constant tempera- 

 ture and per square centimeter surface of each of three crystal faces was deter- 

 mined. The relative water yield per square c. m. for octahedral, cubic and 

 dodecahedral faces at 35°C was 1. : 1.27 : 1.60; at 50°C about four times as 

 much water was yielded, but the relation for octahedral and cubic faces remained 

 nearly the same, viz., 1 to 1.25. a. j. m. 



Qrunling, Fr. Ueber die Mineralvorkommen Dr. Griinling was sent by the Tamnau- 

 von Ceylon. Zeit. f. Kryst, ll\ 200-230, „^.. r -r. i- n • 



inoo. J 7 J7 btiftung of Berhn on a collectmg tour 



to Ceylon in 1896. He describes the 



mineral localities, the history of the occurring species, and the native method of 



cutting, and gives a bibliography and map and statistics of production of 



pearls, rubies, etc. The species obtained included apatite, phlogopite, hydro- 



phlogopite, serpentine, pyrite, spinel, graphite, ruby, sapphire, chrysoberyl, 



zircon, tourmaline, sillimanite, moonstone, garnet, and rutile. a. j. m. 



Melczer, G, Ueber einige Mineralien vorwie- Determines forms and axial relations of 

 gend von Ceylon. Zeit. f. Kryst. 33 : 240- y-, , , , , ,, . . 



262,1900. Ceylon chrysoberyl, as well as twmnmg 



law and optical characters, and com- 

 pares with Brazilian and Siberian chrysoberyls. One crystal of sillimanite from 

 Ceylon was exceptionally fine. It was a transparent^ grayish blue prism, with 

 excellent cleavage in one direction. H=6f G=:3.249. A plate was cut 

 from the center perpendicular to the length, and about '1\ m.m. thick, which 

 gave a beautiful axial figure with /J>z'. In the Abbe Refractometer this 

 yielded : 



