400 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
more taking a leading part in applying tlie Microscope to the study of 
crystallized bodies. Between the years 1806 and 1862, Brewster 
jniblished a long series of memoirs, dealing with the microscopical 
characters of natural and artificial crystals, and the inclusions wliich 
they contain. About the year 1850, too, Mr. Sorby commenced his 
important investigations on the subject, availing himself of the method 
of preparing transparent sections of rocks and minerals which had been, 
shortly before this time, devised by William Nicol. Mr. Sorby’s epoch- 
making memoir, “ On the Microscopical Structure of Crystals, indicating 
the Structure of Minerals and Eocks,” made its appearance in 1858. 
While one group of investigators, following the lines of the early 
work of Brewster and Sorby, have sought to make the Microscope an 
efficient instrument for the determination of minerals, even when present 
in rocks as the minutest crystals or fragments ; others have no less 
diligently pursued the methods which the same pioneers in this branch 
of research have initiated for solving physical and chemical problems 
connected with the formation of crystallized bodies. 
In the hands of Des Cloizeaux, Tschermak, Zirkel, Von Lasaulx, 
Fouque and Michel-Levy, Kosenbusch, and other workers, the Microscope 
has gradually been developed into a splendid instrument of mineralogical 
research ; and the determination of the minutest particles of a mineral 
is now becoming no less easy and certain than that of the largest hand- 
specimens. 
But, at the same time, Brewster and Sorby’s early attempts to solve 
physical and chemical problems by the aid of the Microscope have not 
failed to exercise an important influence on subsequent workers in these 
branches of science. Link, Frankenheim, Klocke, Harting, and espe- 
cially Vogelsang (whose early death was a severe loss to this branch of 
science), have done much towards establishing the science of crystallo- 
genesis upon a firm basis of accurate observation ; and their labours 
have been continued in more recent times by H. Behrens and Dr. Otto 
Lehmann, the author of the work before us. 
As the well-known treatises of Kosenbusch, and of Fouque, Michel- 
Levy, and Lacroix give us an admirable resume of the present state of 
determinative mineralogy, as improved by the application of the Micro- 
scope, so does the work before us contain a perfect summary of the con- 
tributions of the microscopist to the sciences of physics and chemistry. 
It will only be possible, within the limits of an article like the 
present, to indicate briefly the plan of the very comprehensive and, 
indeed, almost exhaustive work, in which Dr. Lehmann has embodied 
the observations of himself and his predecessors in this field of inquiry. 
The first division of the book deals with the construction and use of 
the Microscope ; especial attention being given to forms of the instru- 
ment, like those devised by Nachet and by the author of this work, for 
the special purpose of studying crystallization and other physical and 
chemical processes. 
The second division of the book treats of those physical properties 
of matter which are presented by all bodies, whether in the solid, liquid, 
or gaseous state. Such questions as the polarization and absorption of 
light, the conduction of heat, and the electric and magnetic relations of 
various substances are here dealt with by the author. 
