ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 227 



MICROSCOPY. 



A. Instruments, Accessories, etc.* 

 (1) Stands. 



Beck's "London " Microscope, Regent Model. | — This instrument is 

 shown in fig. 33, and is designed for the most exacting research. The 

 stage is square, 4 in. by 4 in., surfaced with ebonite, and provided with a 

 mechanical stage, with racks and pinions, giving traversing motions of 

 2 in. in the horizontal direction and 1 in. in the vertical direction, each 

 motion being provided with graduations by which the positions of ob- 

 jects can be registered and refound. The mechanical stage is removable, 

 leaving the stage free for large dishes, and four spring-clip holes are 

 provided. An iris diaphragm is set in the thickness of the stage, and is 

 actuated by means of a lever extending to the stage edge. This 

 diaphragm has a slightly curved form, so that when closed to a small 

 aperture it is within one or two hundredths of an inch of the stage level. 

 By this construction the iris may be closed even when an Abbe con- 

 denser in the substage is at its highest position, and when the light from 

 the condenser is in focus upon the object. There is, therefore, no risk 

 of damage being done to the stage iris diaphragm when focusing the 

 condenser, as it does not come in contact with it at any position. The 

 substage is focused by means of a spiral rack-and-pinion adjustment, 

 and is carried on a massive bracket which swings to one side on a strong 

 centre. The condenser (fig. 34) can, therefore, be instantly swung out 

 of the optic axis to one side by means of the same milled head which 

 actuates the focusing adjustment. As soon as the condenser has been 

 racked down to its lowest limit, it swings clear of the stage. The sub- 

 stage is provided with centring screws. The limb of the instrument is 

 made with a large aperture forming a handle, through which the entire 

 hand can be passed for lifting and manipulating the instrument ; no 

 strain is put on any working parts of the Microscope when it is lifted in 

 this manner. The fine adjustment is of a more sensitive pattern than 

 that of the " London " model, being about four times as delicate, each 

 division on the drum representing T ooWo m - This fitting is placed 

 almost directly behind the Microscope body, so that the weight does not 

 overhang the fitting to any great extent, and thus a fine adjustment can 

 be made which, in spite of its extreme delicacy, is equally sensitive to the 



* This subdivision contains (1) Stands ; (2) Eye-pieces and Objectives ; (3) 

 Illuminating and other Apparatus ; (4) Photomicrography ; (5) Microscopical 

 Optics and Manipulation ; (6) Miscellaneous. 



t R. and J. Beck, London, Special Catalogue, 1908. 



