ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



243 



(2) Eye-pieces and Objectives. 



Hensoldt's Micrometer-Oculars.* — These are manufactured with 

 threaded insertions which can be cut to suit customers 1 instruments. 

 Those described below are of a new type, and possess a notably increased 

 field of view. The visible field is given by the angle under which the 

 circumference of the field-diaphragm appears to the eye, and the real 

 field of view is obtained by dividing the visible field by the telescope 

 magnification. Fig. 47 is Hensoldt's orthoscopic micrometer-ocular. 

 The visible field is about 42°, and the image is completely plane and 

 achromatic. The optical combination consists of one double achro- 



Fig. 47. 



Fig. 48. 



matic lens and a bi-convex lens. Fig. 48 is Hensoldt's euryscopic 

 micrometer-ocular. Here the visible field is 45°, and the optical com- 

 bination is two double achromatic lenses. The field is remarkably 

 large, and absolutely colourless and plane. The image-pOint and eye- 

 point are well separated. 



(.3) Illuminating- and other Apparatus. 



Koristka's Complete Apparatus for Macro- and Micro-projection.f 

 The maker's catalogue shows the arrangements for (1) the macroscopic 

 projection of diapositives on glass ; (2) macroscopic projection of opaque 

 objects ; (3) microscopic projection of liquid preparations ; (4) micro- 

 scopic projection of solid preparations. The last of these is reproduced 

 here (fig. 4'J). The light source is a Schuckert lamp with a very sensitive 

 regulator for maintaining absolute constancy at the light focus. The 

 first condenser, the iris diaphragm, the second condenser and trough are 

 easily recognised in the diagram. They are all carried on suitable 

 supports sliding on an optical bench, and have adjustments for keeping 

 the incident beam in the optical axis. The light is then ready for 

 transmission on to the solid object on the Microscope stage, and thence 

 on to the objective. To facilitate the exhibition of numerous slides, 

 the makers have designed a disk pierced with sixteen excentric apertures. 

 The disk is fitted with suitable clips so that sixteen preparations may be 

 affixed in situ, and, the disk being pivoted, these preparations may be 

 brought as rapidly into the field of view as desired. A second disk is 



* Hensoldt and Sons, V\'etzlar, Catalogue, Astronomische-Optik, pp. 5, 6. 

 t F. Koristka, Milan, Catalogue xiii. (1908) Microscopi ed Accessori. 



