ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
265 
Photomicrography in Space. — Dr. Fayel, President of tho Societe 
Linneenne de Normandie, communicated to that Society * a note on this 
subject which we translate : — “ Under the designation of Photography in 
space, Dr. Fayel records a process of his invention which facilitates the 
observation of opaque objects by the Microscope, even with powerful 
objectives, and which he thinks will hence render important service. 
Instead of focusing directly upon the object, Dr. Fayel allows the image 
to be projected on the ground glass of the photographic camera, and then 
removes the ground glass and examines the aerial image with a Micro- 
scope. In order to reduce the labour of adjusting the Microscope, it 
should first be focused very near the plane of the ground glass. The 
image appears so sharp that the minutest relief-forms of the opaque 
object may be observed by manipulating with the fine-adjustment screw.” 
(6) Miscellaneous. 
Liquid Crystals.f — Prof. 0. Lehmann has been able to demonstrate 
the remarkable fact that three organic substances at certain tempera- 
tures, although actually in a liquid state, show strong doubly refracting 
power, and may therefore be regarded as anisotropic crystals. 
All crystals hitherto known consist of solid aggregates. The author 
has previously shown, however, J that some crystals can be made to flow 
when subjected to pressure exceeding the limit of elasticity. This has 
been long known with respect to amorphous bodies like sealing-wax 
and soft glass. Bodies like these pass, by increase of temperature, 
continuously out of the solid into the liquid state, i. e. the limit of 
elasticity gradually diminishes until at a certain critical temperature its 
value is zero. Beyond this temperature the body is liquid, and the 
smallest force is capable of causing it to flow. If a crystal then 
possesses a very low limit of elasticity, it can be made to flow, just as a 
liquid can, by means of a very slight force. The question therefore 
arises whether a crystal could not have an elasticity limit zero, and thus 
be referred no longer to 6olid but to liquid bodies. 
According to the prevailing ideas, which receive their most perfect 
development in the theory of Soncke, this should be impossible ; for this 
theory supposes that the molecules of crystals form regular point systems, 
held in position by the elastic force. The author, however, considers that 
this theory is unsatisfactory when the physical instead of the purely 
geometrical relations of crystals are considered. If the existence of a 
crystal as such depend on a regular distribution of the molecules, long 
continued deformation should at length lead to the production of a body 
not possessing this regular arrangement, i. e. to an amorphous substance. 
Experiments, however, made by the author showed that no amount of 
deformation was capable of converting a crystal into anything resembling 
in any way an amorphous body. Having regard to this slight corre- 
spondence of the theory with fact, the idea of a liquid crystal appeared to be 
justifiable. One distinction between crystalline and amorphous bodies is 
the capacity possessed by the former alone of growth in a supersatu- 
* Bull. Soc. Linneenne de Normandie, iii. (1888-9), p. 13. 
f Pogg. Ann., xl. (1890) No. 7, pp. 401-23. 
X Zeitschr. f. Phys. Chem., iv. (1889) p. 462. 
