o 



358 SUMMARY OF CURRENT RESEARCHES RELATING TO 



takes the photographs. In order to see that the arrangements are 

 collectively working satisfactorily a lateral tube is fitted to the camera 

 so that the film-image can be viewed direct. To enable the operator 

 to have both his hands free for the fine-adjustment or for any emer- 

 gency, the gearing of the camera is not governed by hand motion, but 

 by a motor controlled by the operator's foot. As a light-source a sus- 

 pended incandescent gas-lamp, or an electric arc-lamp, is recommended. 

 If the latter be used, it should be one of the so-called fixed-point arc- 

 lamps with automatic feed-motion. 



Fig. 72, which shows the apparatus as arranged for vertical use, will 

 easily be understood. 



C5) Microscopical Optics and Manipulation. 



Circular Polarization of Liquid Crystals;* — P. Gaubert points out 

 that 0. Lehmann has noticed circular polarization in the case of epipolic 

 lighb reflected by liquid crystals ; while F. Giesel has demonstrated that 

 transmitted and reflected rays are polarized in inverse senses. Investi- 

 gation of these effects has led Lehmann to observe the following 

 phenomenon due to this circular polarization : — If pressure be applied 

 with the point of a needle on the coverslip of a microscopic preparation 

 of a birefringent liquid whose molecules are oriented in such a manner 

 that the optic axis is perpendicular to the glass slip, a black-cross 

 spherolite is formed whose centre coincides with the point touched by 

 the needle. The fibres have a positive or negative prolongation, accord- 

 ing as the liquid crystals are optically positive or negative. In reality, 

 by reason of the pressure, the molecules (at least those which are not in 

 immediate contact with the glass) orient themselves parallel to the glass 

 slip. The phenomenon is easy 'to obtain with viscous liquids. 



(6) Miscellaneous. 



DisplacemeDt of the Particles in Brownian Movement.f — S. Lif- 

 chitz gives experimental reasons for concluding that a very rapid 

 sonorous shock produces in a gas microscopic whirlwinds whose rotatory 

 speed depends on the period of the shock. 



Microscopic Anatomy. J — This text-book of Microscopic Anatomy, 

 by E. A. Schiifer, forms part of the eleventh edition of Quain's Elements 

 of Anatomy. It is unnecessary to say more than that the text is by 

 the Professor of Physiology and Histology in the University of Edin- 

 burgh, that it is thoroughly up-to-date, and i-i illustrated by numerous 

 coloured plates and over a thousand engravings. We mention this as 

 a guarantee of its trustworthiness and general excellence, for the condi- 

 tions of the journal preclude criticism. Fortunately this is not required, 

 and the task of noticing the volume is an easy one. It will form a 

 useful and important addition to our Library, especially to those in- 

 terested in the subject of human histology and cytology. 



* Comptes Eendus, cliv. (1912) pp. 995-7. 



t Comptes Eendus, cliv. (1912) pp. 1084-5 (4 figs.). 



X Text-book of ilicroscopic Anatomy, being pt. 1 vol. ii. of Quain's Elements 

 of Anatomy, 11th ed. Longmans, Green and Co. (1912) pp.738 (1001 text figs, and 

 24 col. pis.). 



