High Power Binocular Eyepiece. 
This binocular eyepiece is made in a form which replaces the ordinary eyepiece so that a 
monocular microscope can be converted into a thoroughly efficient binocular instrument. It is 
well known that the use of the two eyes for microscopic observation prevents fatigue and improves 
the quality of vision. With a binocular the perceptive faculties are more constant during prolonged 
observation than with a monocular, and with the latter, the detection of fine detail is less certain. 
Often however where the worker has already a satisfactory and probably expensive monocular 
microscope, he is disinclined to dispose of it and purchase a new complete binocular microscope. 
The Beck binocular eyepiece solves the problem. It has all the qualities of the binocular bodies 
which are built into microscopes, but is made in a form which permits it to be inserted into any 
microscope. It can be used with all powers and with any standard objectives, and any eyepieces 
of the standard (:917") size. 
The optical construction consists of a prism composed of two right angled prisms cemented 
together which receives the light from the object glass. The cemented surface has a thin 
semi-transparent layer of silver. This divides the light into two complete bundles, one of which 
is directed into each eye. As the full aperture of the object glass is used in each eye, the resolu- 
tion is unimpaired. 
The two tubes of the binocular are inclined at the normal convergence for near objects. The 
principle of converging tubes in binocular microscopes is discussed on page 45 in connection with 
our other forms of binocular bodies and applies in the same way to the binocular eyepiece. 
The interocular distance is variable from 47 to 78 millimetres, and is adjusted by turning 
the two tubes on a common centre, the tubelength remaining unaltered. 
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