. X-ray observations for foreign bodies and their localisation . mm ^fr Illustration 4. two sets of cross wires, and {) a small fluorescent screen.(/) Shows the appearance on the screen when the tube hasbeen accurately centered, the shadows of the two crossesbeing superimposed on the screen and forming one imageonly ; {g) illustrates the screen appearance before centered, the apparatus (m) is removed and replaced bythe diaphragm (/?) (Fig. 2), which closes down on the same X-Ray Observations for Foreign Bodies 9 centre. Fig. 3 shows a convenient method of centering anunder-t
. X-ray observations for foreign bodies and their localisation . mm ^fr Illustration 4. two sets of cross wires, and {) a small fluorescent screen.(/) Shows the appearance on the screen when the tube hasbeen accurately centered, the shadows of the two crossesbeing superimposed on the screen and forming one imageonly ; {g) illustrates the screen appearance before centered, the apparatus (m) is removed and replaced bythe diaphragm (/?) (Fig. 2), which closes down on the same X-Ray Observations for Foreign Bodies 9 centre. Fig. 3 shows a convenient method of centering anunder-table tube or verifying its correctness. On the tabletop is placed a small papier mache box (a ladys powder pufT boxwill do well), across the top of which two wires are stretchedat right angles, while from their intersection hangs a smalt. Illustration 5. a, Anticathode of tube. 6, Path of normal ray. ni i?,Cupule and dia-phragm in position. ,ij, A disc of cardboard, aperture in the centre I in. indiameter. /, A smaller disc, with tiny central perforation, and secondhole for the return of the cord supporting the plumb-bob /. In use thetube stand is adjusted until the cord hangs in the centre of the perforationk, when the plumb-bob may be lowered and the incidence of the normalray recorded. This simple contrivance can be left attached, the metalportion withdrawn to the side during exposure. plumb-bob on a fine cord dipping into oil, with which thebox is partially tilled. If the tube is now brought under this- 10 X-Kay Observations for Foreign Bodies small contrivance, and its projection on the screen viewed withthe diaphragm closed down, a correctly centered tube will givethe appearance shown at O, while a badly centered tube thatshown ^iK. It is impossible to give too much emphasis to theimportance of accurate centering
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Keywords: ., bookcentury1900, bookdecade1920, bookpublisherstlou, bookyear1920
