ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 293 



Microscopic determination of vapour tensions. — Tho method consists in 

 introducing the vapour into a U-tube, one leg of which is closed, while 

 the other is connected with two receivers containing compressed and 

 rarefied air respectively ; for microscopic measurement the U-tube is a 

 capillary, its horizontal part is immersed in a water or paraffin bath, and 

 examined by a Microscope with horizontal tube bent at a right angle 

 near the objective. The use of capillary tubes has the advantage that 

 minute quantities of the substance are employed and can be examined 

 under very high pressures. The observation should be made when the 

 vapour volume is as large as possible in comparison with the expansion 

 of the liquid in contact with it. 



Microscopic determination of the thermal expansion of liquids. — For 

 this purpose a similar apparatus is used except that the U-tube is 

 replaced by another, one leg of which terminates in a funnel and ground- 

 glass stopper, while the other has a horizontal capillary tube projecting 

 from it to contain the experimental liquid. This tube can be maintained 

 at a constant temperature by a water or oil bath, and is observed by the 

 horizontal Microscope ; it is filled by heating to expel the air and then 

 forcing the liquid in by pressure from one receiver ; the superfluous 

 liquid is then removed and the remainder of the tube filled through the 

 funnel by suction from the other receiver with some coloured fluid. 

 Coloured glycerin, for example, may be used in examining the expansion 

 of carbon disulphide, the movements of the point of junction between 

 the two liquids being followed by the horizontal Microscope. 



Microscopic determination of compressibility . — For this tho author uses 

 the Cailletet apparatus ; tho liquid is contained in a vessel like a 

 thermometer, the end of which is inserted into the glass capillary used 

 for liquefying gases. 



Klaatsch, H. — Ein neues Hilfsmittel fur mikroskopische Arbeiten. 



[Radial micrometer.] Anat. Anzeiij., 1S87, pp. 632-4. 



(4) Photomicrography. 



Photomicrography of Chemical Preparations.* — Dr. 0. Lehmann 

 recommends the use of oblique illumination and the colouring of the 

 preparations ; in photographing crystals it is important that they should 

 appear upon a dark ground, and this is best effected by the Tcipler con- 

 trivance as constructed by Seibert, in which half the field is darkened by 

 a screen below the stage, and the other half by a screen above the eye- 

 piece. As crystals cannot be coloured like organic preparations, it is 

 best to use polarized light with doubly refracting crystals at any rate. 

 By using the nicols parallel, or not crossed, the crystals are made to 

 appear bright, dark, or coloured upon a bright or dark field. 



Neuhaus's Photomicrographic Camera. — Dr. E. Neuhaus's camera 

 is claimed to be distinguished from others which serve the same purpose 

 by the fact that it can be extended to the length of 180 cm., and that the 

 focusing of the Microscope can be simply effected for any length of the 

 camera. 



It consists of bellows 1^ metre in length divided into two parts, so 

 that one can be kept compressed when the other is completely extended, 

 and it can be clamped at any desired length. The guides in which the 



* Loc. cit. 



