32 



TROWBRIDGE. 



urements are 1 1 centimeters in width by 7.5 centimeters in depth, 

 while at the opposite end, at C, the casing is square, being 7.5 

 X 7. 5 centimeters. 



Just back of the end C, the lower portion of the casing is en- 

 larged by a half-cylinder or half-drum extension of 6 cms. 

 radius, which was added so as to conform the shape of the casing 

 to certain devices which comprise a part of the interior con- 

 struction of the apparatus. The entire inside of the instrument, 

 including all the brass parts, is painted a dead black. 



i), in figs. 8 and 9, is a binocular eye-protector of patent 

 leather, which is shaped to fit above the eyes, and has a black 

 velvet cushion on the edge, marked B' . This cushion is added 

 so as to prevent, as far as possible, all light from entering the 

 instrument from around the edge of the eye -protector. It 

 is made soft and elastic, in order that it may readily be made to 

 follow the contour and set close to the face of the person using 

 the instrument. 



At the opposite end from ^ is a brass screen holder, C, which 

 measures 7.5x7.5 centimeters, and is constructed to fit exactly 

 into the end of the casing A. In this screen holder there is a 

 circular aperture 5.5 cms. in diameter, which is encircled by a 

 thin ring of brass that extends .5 cms. outward from the main 

 portion of the screen holder. A screen of black paper is placed 

 over this opening, having on its inner side crystals of barium-plat- 

 ino-cyanide (BaPtCy^ + 4Aq), tungate of calcium (CaWOJ, or 



n N 



Fig. 9. Top View of the "X-Ray Detector." 



