. Machinery and processes of the industrial arts, and apparatus of the exact sciences. their due proportion on turn-ing a single milled head. This form of the binocular microscope is at- Pig- HO. tended with an advantage pecidiar to itself. Ithas been observed above that true stereoscopicvision requires that the two halves into which thecompound pencil is divided behind the objectiveshould cross each other, so that the right eye mayreceive the left-hand half and the left eye theright-hand half. The rectangular prism when in-troduced through the side of the body must there-fore be advanced so f
. Machinery and processes of the industrial arts, and apparatus of the exact sciences. their due proportion on turn-ing a single milled head. This form of the binocular microscope is at- Pig- HO. tended with an advantage pecidiar to itself. Ithas been observed above that true stereoscopicvision requires that the two halves into which thecompound pencil is divided behind the objectiveshould cross each other, so that the right eye mayreceive the left-hand half and the left eye theright-hand half. The rectangular prism when in-troduced through the side of the body must there-fore be advanced so far as to reflect the oppositehalf of the compound pencil, while it leaves theadjacent half free to pass. But if this prism, ofwhich the position can be controlled by means ofa slider, is drawn toward the extra tube so as to parts separated, reflect the nearer half of the compound pencil and to allow the oppositehalf to pass freely, the conditions will be such as to produce pseudoscopicvision, and to present an image in which the reliefs shall appear as Nachets Binocular 540 PARIS UNIVERSAL EXPOSITION. depressions and the depressions as reliefs. In the examination of an objectof obscure structure, the contrasts of appearance thus presented are oftenvery serviceable in contributing to the formation of correct is a disadvantage common to all the forms of binocular microscopeabove mentioned that they perform well only with objectives of com-paratively low power. In fact, it is obvious that a performance theoret-ically perfect would require not only that the division of the compoundpencil emerging from the objective should be exactly equal, but thateach of the simple pencils of which the compound pencil is made upshould also be equally divided. Such an equality could only be per-fectly secured by making the division in that plane or cross-section inwhich the axes of all the simple pencils cross, which would be really theplane passing through the centre of t
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Keywords: ., bookcentury1800, booksubjectmachinery, booksubjectscientificappa
