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SUMMARY OF CURRENT RESEARCHES RELATING TO 



image would be out of focus when the other was sharp. The focus is 

 corrected in the Beck Binocular by combining a parallel plate of glass 

 of the required thickness with the right-hand prism : thus equality in 

 the focus and in the magnifying power of the two images is ensured. 

 The binocular prism is carried in a sliding box in the body of the Micro- 

 scope (fig. 22). By sliding it out of the optic axis the Microscope is 



Fig. 22. 



converted into a monocular instrument, or by unscrewing the knob 

 (F, fig. 22) it can be slid completely out of the Microscope for clean- 

 ing or dusting. It is quite safe to remove the prism complete in its 

 box, as it returns with accuracy to its exact position, and the adjust- 

 ment will not be interfered with. The fact that when the prism moves 

 to one side the instrument becomes absolutely the same as a monocular 

 Microscope renders this Microscope equally useful for photography, 

 drawing, micrometry, or any other purpose. 



The construction of this binocular renders it possible to retain the 

 short tube of the compact monocular Microscope. When the draw-iubes 



