ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 205 



will readily suggest themselves to the laboratory worker. Further 

 details include a small fixed illuminating lamp placed in such a position 

 as will best illuminate the object. The 25, 40, and 48 mm. paired 

 objectives with the and III paired oculars are particularly suited for 

 the examination of fractures, etc., at varying magnifications. 



R. and J. Beck's New Binocular Microscope.* — The makers of 

 this instrument (fig. 22) summarize its advantages thus : (1) resolution 

 equal to that of monocular: (2) equal illumination, both eyes; (3) equal 

 optical path and magnification, both eyes ; (4) converted into a mono- 

 cular by a touch ; (5) prism removable for cleaning ; (6) short tube 

 length, compact microscope ; (7) no special object-glass or oculars, no 

 special requirements ; (8) simple adjustment for interocular distance ; 



(9) the standard angle for convergence, ensuring perfect comfort ; 



(10) stereoscopic vision ; (11) binocular vision, saving eye-strain and 

 giving; better results than monocular vision. The vital element in a 

 binocular is, of course, the prism, and in this respect Messrs. R. and J. 

 Beck have introduced a novelty which is responsible for most of the 

 advantages claimed above. The prism is shown separately in fig. 24, 

 and is placed above the object-glass. The whole of the light from the 

 object-glass passes through the surface of the glass B A to a surface 

 E A, which is coated with a semi-transparent surface of silver. This 

 allows part of the light to pass through and part to be reflected into the 

 second tube of the Microscope as shown by the dotted lines; thus the 

 full-size beam goes to form each image and no lack of resolution occurs. 

 Two perfect pictures are produced, one in each eye. As the transparency 

 and reflecting power of the surface E A can be regulated according to 

 the amount of silver that is deposited, the relative intensity of each 

 image can be made identical, and the right- and left-hand images are 

 equal in brilliance. As to the intensity of tbe mental impression, it 

 has been urged that when au initial body of light is divided into two 

 parts, and one part is sent into each eye of the observer, the effect of 

 brilliance is the same as if the whole light be directed into one eye 

 only. Certainly there is some reason for this argument, though it may 

 be an over-statement of the case. It is, however, no disadvantage if a 

 slightly stronger light is required with a binocular than a monocular 

 Microscope. The monocular observer, iu order more readily to con- 

 centrate his attention on the employed eye, is apt to use an illumination 

 that is far too brilliant, to the detriment of his eyesight. In the use of 

 the binocular both eyes are equally stimulated, and there is no tempta- 

 tion to use excessive illumination, and theory goes to show that a low 

 illumination is more efficient for displaying fine detail. The diagram 

 of the binocular prism (fig. 24) shows that the distance from the surface 

 E A, where the beam of light is divided into two portions to the two eye- 

 pieces, is not of equal length ; the light on the right-hand side has to 

 travel a distance 6H farther than the light that passes directly through. 

 It would, therefore, not be possible to focus both beams of light to the 

 same points in the two eye-pieces : if this were not compensated, one 



* Special Catalogue : The Beck Binocular Microscope. Messrs. R. and J. 

 Beck, London, 20 pp. 



April 15, 191 4 p 



