. Radiography and radio-therapeutics . ng theexact extent of the displacement for different objects will greatly add tothe value of the stereoscopic plates he produces. After the exposure and subsequent development the two images mustbe optically fused into one, and for this purpose there are many forms ofinstrument, such as the WTieatstone and the Scott-Dean reflecting stereo-scopes, and the Pirie hand stereoscope. The pictures can be reduced andviewed in a hand stereoscope. Good stereoscopic negatives, when \aewed in position, show perfectpictures, with the correct perspective for the parts
. Radiography and radio-therapeutics . ng theexact extent of the displacement for different objects will greatly add tothe value of the stereoscopic plates he produces. After the exposure and subsequent development the two images mustbe optically fused into one, and for this purpose there are many forms ofinstrument, such as the WTieatstone and the Scott-Dean reflecting stereo-scopes, and the Pirie hand stereoscope. The pictures can be reduced andviewed in a hand stereoscope. Good stereoscopic negatives, when \aewed in position, show perfectpictures, with the correct perspective for the parts showTi, though theexact locaUsation of a foreign body may be difficult or in some instancesimpossible. A Wheatstone stereoscope, or its modified Scott-Deanform, should be employed whenever possible as it affords valuable aid,by means of its adjustable parts, in quickly getting the correct position ofthe plates. When this comparatively elaborate stereoscope is not available,a Pirie hand stereoscope will be found useful. 150 KADIOGKAPHY. 2 1 3 2 Fk;. 121.—Diagram to illustrate the piineipleof Wheatstones reflecting stereoscope.(From Ency. Brit.) K K, right and left eyes ; S S S, mirrors ;P P, objects in position ; a b, picture on leftside ; b, Bj, picture on right side ; 3 2 1,corresponding points on retina ; A L B, objectas seen in relief in mirrors ; h, picture seen byleft eye in position B, and image on retina at 3 ;c, seen at L R, and retinal image at 2 ; a, seenat A, anil retinal image at 1 ; a^, seen at A,and retinal image at 1 ; Cj, seen at R L, andretinal image at 2 ; fej, seen at D, and retinalimage at 3. stereoscope which generally holds the Another form of stereoscopewhich is of great value in X-raywork is that introduced many yearsago by Sir David Brewster. Theinstrument is very convenient forthe inspection of reduced picturesof stereoscopic radiographs. Theseare readily produced in a reduc-ing lantern. For small objects, suchas fingers, wrists, temporal bonesand ac
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