. Dental and oral radiography : a text book for students and practitioners of dentistry . differ-ent from gas in its properties as ordinary air orgas is different from a liquid. He found that theimpact of the cathode rays against the wall ofthe tube would produce within it a greenishphosphorescence or florescence and an in-crease in temperature; also that these rays couldbe intercepted by metallic plates within the concentrating the rays at the focus of a con-cave cathode, he was able to produce a brilliantflorescence and a very high temperature, both atthe walls of the tube and in var
. Dental and oral radiography : a text book for students and practitioners of dentistry . differ-ent from gas in its properties as ordinary air orgas is different from a liquid. He found that theimpact of the cathode rays against the wall ofthe tube would produce within it a greenishphosphorescence or florescence and an in-crease in temperature; also that these rays couldbe intercepted by metallic plates within the concentrating the rays at the focus of a con-cave cathode, he was able to produce a brilliantflorescence and a very high temperature, both atthe walls of the tube and in various substanceswithin it. Without doubt, Sir William Crookesunconsciously produced the x-ray in the courseof these experiments. In 1892 Prof. Heinrich Hertz discovered thatcathode rays would penetrate gold leaf and other 2-4 DENTAL AXD ORAL RADIOGRAPHY thin sheets of metal placed within the tube. Soonafter this discovery, Hertz died, and his experi-ments were continued by his assistant, Lenard,who was able to demonstrate that many of thephenomena of the cathode rays could be observed. Fig. 3. Sir William Crookes. outside of the Crookes tube. By closing a vacuumtube at the end opposite the cathode with a thinsheet of aluminum, he demonstrated that a radia-tion proceeded through or from the aluminumwalls of the tube which would pass through manysubstances opaque to ordinary light, and after NATURE OF X-RAY AND ITS DISCOVERY 25 passing through such substances, it would exciteflorescence in crystals of barium platino-cyanide,and would effect sensitive photographic plates inmuch the same manner as ordinary light. Lenardconsidered that all these phenomena were dueto the cathode rays alone although in the light ofour present knowledge, there is no doubt thatnot only in his experiments but in those ofCrookes, Hertz, and other investigators, x-rayswere produced. However, they were not recog-nized as such until 1895 when Prof. Rontgen star-tled the world by the announcement of his dis-co
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