468 The American Naturalist. [May, 
else has developed the elegant and accurate methods of etching crys- 
tals, gives us in the introduction of this work a most admirable resumé 
of the work that has been done and the methods that are in common 
use. Not only etched figures (Aetzfiguren or Aetzgriibchen), but 
v. Ebner’s Lésungsgestalten, Hamberg’s Prarosionsflichen, and Becke’s 
Lésungsoberflichen are discussed. The studies of Meyer, Penfield, 
and Gill, on the forms derived by prolonged etching of spheres of 
quartz with hydrofluoric acid and the alkaline carbonates, and those 
of Hamberg on forms assumed by cylinders of Iceland spar etched 
with hydrochloric acid, are correlated. The author discusses in detail 
the application of the methods of etching to the determination of iso- 
morphous relations. The greater part of the work is devoted to de- 
tailed descriptions of a number of important minerals on which the 
study of etched figures has been of special significance. Among these 
are the minerals: cryolite, apatite, Zinnwaldite, dolomite, nepheline, 
datolite, leucite, and boracite. The plates are particularly beautiful, 
and are suited to lecture demonstration. 
Czapski. Theory of Optical Instruments.’—Mineralogists 
and petrographers who have occasion to test the working or to deter- 
mine the constants of compound microscopes, will find this recent work 
of the scientific expert of the Zeiss Optical Works at Jena of much 
practical utility. -The greater part of the work is devoted to a compli- 
cated mathematical exposition or Abbe’ s Mano bead optical instru ments» 
this latter term bei which 
form images of external objects, chief among which are the eye, camera 
lens, microscope, and telescope. The portion, however, which will find 
most use among mineralogists and petrographers, is included in the 
last two chapters. Here the compound microscope, with its modern 
accessories, is described in respect to construction and use, and methods 
are given for the practical determination of its optical constants. 
Fuess. Instrument Catalogue.*—R. Fuess, the well-known 
goniometer and microscope maker, has issued a supplement to his 
catalogue of 1891. The supplement treats of goniometers, universal 
apparatus, microscopes (with many recently devised attachments), 
grinding apparatus, mounting materials and collections of thin sections. 
™Theorie der optischen Instrumente nach Abbe, von Dr. Siegfried Czapski: 
Trewendt, Breslau, 1893. Price, M. 9.60. (Reprinted from Vol. II of Winkel- 
mann’s Handbuch der Physik.) 
8 Ergänzungen zum Preis-Verzeichnisse 1891, über krystallographische und 
petrographische Instrumente, von R. Fuess, Berlin-Steglitz, 1894. Pp. 56 
