764 SEC. 18. BIOLOGY. 



3533a. Microscope Stand, with modification of Jackson's 

 limb, Wenham's binocular body, a concentric rotating stage, and 

 Brown's iris diaphragm. R. fy J. Beck. 



3534. " The Educational Microscope." The first cheap 

 microscope supplied with English object glasses. Prepared for 

 and exhibited in the Paris Exhibition of 1855 by Smith, Beck, 

 and Beck. J. Beck. 



3535. " Universal Microscope." This instrument, made 

 for the Exhibition of 1862, showed a new method of varying the 

 object glasses and eye-pieces without removing them, the mode of 

 constructing a simple binocular body, and a loose lever as a slow 

 motion. R. $ J. Beck. 



3536. " The Popular Microscope." The first cheap 

 binocular microscope brought out in this country, in 1864. 



R. $ J. Seek. 



3537. " The Economic Microscope; " a working instru- 

 ment when the binocular arrangement is not required. 



R. Sf J. Beck. 



3538. " Darwin's Dissecting Single Microscope." 



R. $ J. Beck. 



3538a. Sorby's Binocular Spectrum Microscope, with 

 his new apparatus for measuring the wave length of every part of 

 the spectrum. R. $ J. Beck. 



3539. " Beck's Dissecting Single Microscope." 



R. $ J. Beck. 



3540. Stephenson's Erecting Binocular Microscope. 



J. W. Stephcnson. 



The primary objects of this microscope are, as the name implies, the 

 erection of the image and the utilization of deep powers by the binocular. 

 The binocular effect is produced by the use of two equilateral prisms, placed 

 together at an angle of 4 30' ; the two edges in contact form a wedge by 

 which the cone of light from the objective is divided, and, after internal total 

 reflection, is laterally inverted. The divided pencil of light is then received 

 on a plate of silvered glass at the polarizing angle, the reflection from which 

 completes the erection of the image. This plate, which is of black glass, 

 rotates on its axis, the black side being instantly exchanged for the silvered 

 side, when an analyzer is required. 



The advantages of this instrument are, 



1 . The erection of the image. 



2. The small angle (9) at which the bodies converge, giving a con- 

 vergence towards an imaginary point at a distance of 14 to 15 inches 

 from the eye. 



3. A horizontal stage, with the bodies inclined at a convenient angle. 



4. The immediate substitution of an analyzing plate of black glass when 

 polarized light is used. 



