52 THE USE OF THE MICROSCOPE 



seems in sonic respect superior to the Grcenough binocular; 

 l^ecause its objectives are usually of higher aperture, and 

 doubtless better corrected; and because over the whole 

 field both halves of the objective focus equally. Its dis- 

 advantages are : that it does not give simultaneously perfect 

 resolution and the strongest stereoscopic effect; that it 

 cannot apparently be used at its best stereoscopically with 

 objectives much lower than 0.3 in aperture (Carpenter, 

 1875); and that it cannot be used for dissection without 

 special practice, because of the inverted picture, unless 

 erecting prisms are incorporated (or erecting lenses, as in 

 the Lihotzky eyepiece attachment). 



Binocular Attachment. — The Siedentopf binocular attach- 

 ment (now made in some form by most optical firms) 

 with a concave achromatic amplifier between the objec- 

 tive and the prisms, will convert a monocular micro- 

 scope into a monobjective binocular. It is equal to the 

 binocular without amplifier. (The Bitukni slanting attach- 

 ment and other oblique eyepieces allow the stage to be 

 kept horizontal when dealing with liquids.) 



It is the writer's opinion, after several years' experience 

 with the binocular and the binocular attachment, that 

 better work, and more work, can be done with the binocular 

 than with the monocular microscope ; even if all precautions 

 are taken to shield the unoccupied eye in the latter case. 



History. — The monobjective binocular of the modern 

 type was, as already noted, apparently based on Abbe's 

 binocular eyepiece (10), as modified by Ives. Jentzsch 

 perfected his model about 1913 (76). Siedentopf has 

 introduced improvements, especially in the mode of 

 adjustment for interocular distance. For the literature, 

 see especially the two papers of Abbe on binocular vision 

 (10, 12), and Jentzsch's paper in the Journal of the Royal 

 Microscopical Society for 1914. 



Summary. — This binocular depends on a layer of silver 

 or platinum which reflects half and passes half of the 

 incident light. The instrument is best used without strong 

 stereoscopic effect. It has otherwise most of the advan- 



