ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



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transparent celluloid, which are adapted to be moved in fan-wise 

 fashion about a pivot-piece g screwed to the condenser rim. By moving 

 one or more of these coloured strips over the condenser, the desired 

 colour-effect upon the object may be attained. 



Bausch and Lomb's Filar Micrometer.* — This micrometer (fig. 53) 

 consists of a series of ruled lines 0*5 mm. apart, with every second 

 graduation number up to ten in either direction from a long centre line. 

 This scale is mounted with an eye-piece, and its position with reference 

 to the edge of the image may be regulated by means of the milled head 



Fig. 53. 



shown at the right in the illustration. A complete revolution of the 

 micrometer-screw moves the cross-hair a distance of 0*5 mm. upon 

 the scale. 



Schmidt and Haensch's Special Episcope.f — This apparatus is 

 intended for the projection of large illustrations, engravings, maps, etc., 

 up to a magnitude of 40 X 40 cm. 



As will be inferred from fig. 54, the apparatus essentially consists of 

 a steel box containing an arc-lamp, a lens system, and a water-cooler. 

 There is also an easily adjustable metal plate 65 x 65 cm. : also, two 

 objectives in association with two plane front-silvered mirrors. A cloth 

 curtain effectually screens any three sides, so that pictures, etc., may be 

 introduced from any desired fourth side. The arrangement of the 

 individual parts and the ray-path are shown in fig. 55. In order to 

 attain an increased brightness of image two arc-lamps of 35 amperes 

 are inserted, one behind the other. The second lamp and condenser 

 are not visible in the figure, as they lie directly behind L x and K^ 

 This duplex arrangement is recommended as being more effective, and 

 as requiring no greater consumption of current than in ordinary forms 

 of such apparatus. To avoid unnecessary waste of light the rays after 



* Bausch and Lomb Optical Co., Rochester, N.Y., Catalogue, Microscopes and 

 Accessories, p. 61. 



f Deutsche Mechaniker-Zeitg. (Nov. 1908) pp. 213-16 (2 figs.). 



