ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
401 
The next division relates to the peculiar properties presented by 
solids. Elasticity and plasticity are considered, and, under the latter 
head, the remarkable phenomenon of the production of twinned structures 
in crystals by mechanical means is fully discussed. Under the head of 
cleavage we find a treatment of such phenomena as the production of 
mathematical figures in certain crystals by pressure, percussion, &c. ; 
while under the heads of “ Enantiotropie ” and “ Monotropie ” are 
classified the consequences which follow from heteromorphism among 
crystalline substances, and the tendency of the heteromorphous forms to 
pass one into the other. 
The division dealing with liquids and their peculiar properties 
contains discussions on fluidity, surface-tension, diffusion, capillarity, 
and crystal-growth, with the origin of structural anomalies. The 
problems of solution and precipitation, with those of solidification and 
fusion, are also treated of in this part of the treatise. 
The second volume of the work commences with the discussion of 
the properties of gases and their relations to solids and liquids. This 
division of the subject, which is very exhaustively treated, extends to 
335 pages. 
The work concludes with critical remarks upon different molecular 
theories. The chapters dealing with the theories of crystal structure, 
of allotropy, of heteromorphism, and of isomerism, with several others, 
in tlie same division of the book, are full of interest and suggestiveness. 
A supplement of about 150 pages is devoted to what the author 
calls “ crystal-analysis,” or what is generally known to geologists and 
mineralogists as “ microchemical analysis.” Very minute particles of 
an unknown substance may often be determined by being treated with 
appropriate reagents and studied under the Microscope ; in this way 
they are made to yield crystals of various compounds w'hich can be 
recognized by their characteristic forms and habit. An admirable 
summary is given by the author of the work of Borieky, Streng, Behrens, 
Haushofer, and others, who have gradually perfected this branch of 
research, and made the method one which is of the very greatest service 
to the students of microscopical mineralogy and petrography. 
While the physicist and chemist will find in this work a perfect 
mine of interesting and ingenious experiments (many of which are suited 
to class-demonstrations by projection methods), the mineralogist and 
geologist will hail the appearance of the book as one that completes 
and supplements the well-known treatise of Vogelsang — a work that has 
exercised the most important influence on the development of petrological 
theory. 
In conclusion, it may be pointed out that, not only are the numerous 
observations of the author on crystallogenesis that are described in 
memoirs in ‘ Groth’s Zeitschrift ’ included in the work before us, but 
many others that have never before been published find a place in these 
volumes. The work is very fully illustrated both with woodcuts and 
coloured plates, and constitutes a complete synopsis of all that is known 
on a number of questions of great importance and interest to workers in 
many different branches of science. 
2 F 
1890. 
