Identifier: dentaloral00mcco (find matches)
Title: Dental and oral radiography : a text book for students and practitioners of dentistry
Year: 1916 (1910s)
Authors: McCoy, James David
Subjects: Radiography, Dental X-rays Teeth Mouth
Publisher: St. Louis : Mosby
Contributing Library: West Virginia University Libraries
Digitizing Sponsor: LYRASIS Members and Sloan Foundation

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at potential. As early as 1838 he con-ducted a series of experiments to determine theeffect of electrical discharges upon rarified gases,and invented the terms anode and cathodefor positive and negative electrodes. In 1857 Geissler constructed the first vacuumtubes and it was noted at this time that an elec-trical discharge passed through these tubes wouldproduce a peculiar glow or phosphorescence, thecoloring of which depended upon the characterof the rarified gas contained in the tube. Thisphenomenon became known as florescence. A few years later (1860) Prof. HittofT, a cele-brated physicist of Minister, conceived the ideaof exhausting the Geissler tube to a higher de-gree of vacuum and found as a result an increasedresistance to the passing of the electrical dis-charge, and that the color of the rarified gases 22 DENTAL AND ORAL RADIOGRAPHY under florescence, varied with the degree of rari-fication. He also discovered another fact whichwas to have an important bearing upon the work
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Fig. 2.Michael Faraday. of later experimenters, and that was that the lum-inous discharge in a Geissler tube, could be de-flected by a magnet. NATURE OF X-EAY AND ITS DISCOVERY 23 The important work of these early experimen-ters was followed later (1878) by Sir WilliamCrookes, who succeeded in constructing a moreperfect vacuum tube, that is, one which could beexhausted to a much higher degree of vacuum.With these improved tubes, Crookes discoveredthat with a sufficiently high vacuum the luminousglow within the tube disappeared, and demon-strated that within it there was a rectilinear radi-ation from the cathode, which he conceived as be-ing a projection of particles of highly attentuatedgas at exceedingly high velocity. To this radiationhe gave the name Cathode Rays, and becauseof the peculiar behavior of gas in this exceedinglyrarified state, he concluded that it was as differ-ent from gas in its properties as ordinary air orgas is different from a liquid. He found that theimpact of

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