ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



371 



2 downwards the holes serve as stops. The centre of hole 2 coincides 

 with that of hole 1 when the spring-catch S t engages into the nick I. 

 The centres of the holes are arranged heptagonally in a circle, and the 

 object of introducing this diaphragm with its range of eight grades was 

 to replace the iris-diaphragm, usually placed between the polariser and 

 the mirror, and at the same time to render it available as a Wright's 

 slider. The diameters of the apertures are engraved on the disk in terms 

 of millimetres. 



In the construction of the Microscope due allowance has been made 

 for its practical applicability to photomicrography, and the stand may 

 accordingly be employed with Leitz' New Universal Photomicrographic 

 Apparatus. Besides photographs of the usual character, stereoscopic 



Fig. 92. 



views of inanimate objects (e.g. crystals) may be obtained. For this 

 purpose the object is successively displaced laterally 32 mm. to the left 

 and to the right of the middle line and sharply focused, a photograph 

 being taken in each position. A stereoscopic dark-slide has the ad- 

 vantage that both exposures may be made on one plate, without which 

 it is difficult to obtain uniformly developed negatives or even prints. 



Leitz' Museum Microscope* — Leitz' Museum Microscope is a 

 simple apparatus for showing persons unacquainted with the use of the 

 microscope a series of specimens. In this instrument (fig. 93) the stage 

 is replaced by a drum capable of rotation from left to right, and pro- 

 vided with supports for twelve preparations, which are retained in 

 position by clips. Another detachable drum of sheet-metal serves to 

 preserve the specimens from damage. Both drums are perforated by 



E. Leitz* Catalogue, No. 42 (1907) p. 63 (1 fig.). 



2 C 2 



