236 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the object-stage. The stand is hinged with a clamping lever. The 

 coarse adjustment is by rack-and -pinion ; the fine by a micrometer 

 screw, whose head is divided for thickness measurements (1 division = 

 0*01 mm.). The draw-out tube has millimetre graduations. The 

 object-stage is circular (diameter 105 mm.) and rotatory; the rim is 

 graduated and has a vernier. Under the stage is a screw for securing 

 the rotatory plates. For orientating the object two radii perpendicular 

 to one another are scored on the stage. Centring is performed at the 

 lower end of the tube by two fine screws. The illumination is effected 

 by concave and plane mirrors with universal movement. There are 

 two analysers. One, provided with graduations and verniers, is applied 

 above the ocular ; the graduated disc belonging to it being placed 

 close to the ocular end of the draw-tube. The second analyser can be 

 pushed in and out of the tube immediately above the objective without 

 being detached from the tube. The change in the focal length of the 

 objective due to the insertion of the analyser is rectified by the applica- 

 tion of a lens of long focus over the prism, so that after the insertion 

 of the analyser no new adjustment of the object is necessary. The 

 inner nicol of the second analyser is rotatory, and a graduation shows 

 its position. The prisms of the analysers have right-angled end-planes, 

 and give a maximum field of view. The polarizer is placed in a push- 

 sleeve under the object-stage ; at other times this sleeve may contain 

 diaphragm-holders; it is provided with a lever arrangement for con- 

 venient elevation and depression. The rotation movement of the nicol 

 is controlled by a screw working in a slot. Over the polarizer a double 

 condenser is placed for axial images. The polarizer can be exchanged 

 for a cylindrical mounting provided with three diaphragms of various 

 diameters. A Bertrand lens for the magnification of axial images can 

 be used with the ocular, and is slipped into the tube from above into 

 the position of the diaphragm of the draw-out tube. The oculars are 

 all provided with cross-threads, and specially designed for polarizing 

 work ; a screw engages in a notch in the tube and so fixes the direction 

 of the cross-threads, this direction being rendered visible by a mark on 

 the outer rim of the mount. Other marks are placed on the side of the 

 ocular at angles of 45° to the cross-threads in order to reveal the 

 direction of minimum elasticity in the application of the gypsum plate. 

 The illustration shows the objective and condenser, fitted with Wein- 

 schenk's pliers, which hold the lens firmly to the tube, and yet allow a 

 rapid and easy exchange. 



"Voinow, D. N. — Principii de Microscopic. Bucaresci (Gobi), 1901, 8vo, 271 pp. 



(2) Eye-pieces and Objectives. 



Hastings Apochromat.* — A. A. Adee, after testing the 5 mm. apo- 

 chromatic objective designed by Prof. Hastings of Yale University, 

 speaks very highly of its performances in difficult photomicrography. 

 He finds it superior in working quality to any apochromatic lens he 

 has yet tried, except the Zeiss apochromat of 4 mm. ; and, as regards 

 that, the Hastings lens holds its own in photomicrography. The 



* Journ. App. Micr., 1901, pp. 1442 and 3. 



