A manual of X-ray technic (1917) (14571264088)

Identifier: manualofxraytech1917chri (find matches)

Title: A manual of X-ray technic

Year: 1917 (1910s)

Authors: Christie, Arthur Carlisle, 1879-

Subjects: Radiography, Medical Diagnosis, Radioscopic X-rays Bones Gastrointestinal system Radiography Bone Neoplasms Gastrointestinal Diseases

Publisher: Philadelphia London : Lippincott

Contributing Library: Francis A. Countway Library of Medicine

Digitizing Sponsor: Open Knowledge Commons and Harvard Medical School

Text Appearing Before Image:

f a conductor is directlyproportional to its length and inversely proportionalto the area of its cross-section or square of its diameter. A rheostat is an appliance used to vary thestrength of a current by changing the amount of theresistance. For Rontgen-ray apparatus, rheostats areusually made of a number of coils of German silverwire. In Fig. 21 the dots represent contact-points towhich the movable arm may be shifted. Nos. 1 and 2are connected at the bottom, 2 and 3 at the top, andso on. The leading-in current enters at H and whenthe movable arm is set on the first contact point thecurrent passes through A, down coil No. 1, up coilNo. 2, down No. 3, and so on until it passes out at B.Shifting the arm to the second point eliminates coilNo. 1 from the circuit and reduces the amount ofresistance, thus increasing the strength of the current. EXCITING THE RONTGEN-RAY TUBE 49 Resistance may thus be gradually reduced by shiftingto successive points until the last one is reached and 12 3 A

Text Appearing After Image:

Fio. 21.—Rheostat. the current flows directly from H through the mov-able arm to B, the rheostat no longer being in thecircuit. CHAPTER VI. RoNTGENOGRAPHY. The Rontgen ray acts upon sensitized plates likeordinary light, therefore the making of rontgenogramshas much in common with photography. It mustalways be remembered, however, that whereas thephotograph is produced by the action of light whichis reflected from the object to be photographed, therontgenogram, on the other hand, is a record of thepenetrability of the different parts of the object to theRontgen ray. The photographic plate consists of a piece ofglass coated with gelatin containing sensitive silversalts. The salt may be either the bromide, the chlo-ride, or the iodide of silver. The iodide is not oftenused except occasionally as an addition to thebromide, and the chloride is used only for slow emul-sions such as are used on printing-out paper and forlantern slides. The gelatin-bromide emulsion, eitherwith or without th

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1917

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