St. John, Thomas M. (Thomas Matthew), b. 1865 · New York, T. M. St. John · leaf 148
^ considered opaque. The hand, for example,maj be used as a negative for producing a photograph ofthe bones, as the raj^s do not pass equally well throughflesh and bone. X-RAYS—HUMAN BONES PHOTOGRAPHED. 145 Fig. 220 shows a Crookes tube fitted with a metal plate,so that the cathode rays coming from… … Fig. 222. invisible and are even given out where the cathode raysstrike the glass. Some chemical compounds are madeluminous by these rays; so screens are made and coatedwith them in order that the shadows produced by the
Electricity
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