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Scientific Proceedings (65). 



incomplete vacuum. A high potential current passes in the tube 

 from the anode to the kathode, frees the electrons of the latter and 

 propels them towards the antikathode or target. The bombarding 

 of the electrons induces the formation of the Roentgen rays on the 

 surface of the target. The target is built of platinum and becomes 

 overheated under the action of the kathode rays. The heat frees 

 the gases in the platinum, and these in turn diminish the vacuum 

 of the tube. As a consequence the velocity of the kathode rays 

 also diminishes and the Roentgen rays become softer. Various 

 regulating devices are added to the tube in order to keep the char- 

 acter of the Roentgen rays uniformly hard for a sufficiently long 

 time to produce a biological action. Still the penetration of the 

 rays emitted by the tube constantly changes. The fundamental 

 advantage of the Coolidge tube consists in the fact that it has a 

 nearly complete vacuum so that the small amount of gas escaping 

 from a heated target can not influence it. Moreover the target 

 is built of tungsten which is freed of gas with greater ease before 

 the tube is built. In such a tube with a very complete vacuum 

 high potential current can not pass from the anode to the kathode 

 and free the negative electrons of the latter. The freeing of the 

 kathode rays is accomplished in the Coolidge tube through the 

 heating of the kathode to a very high temperature by the aid of a 

 special storage battery. The kathode consists of a spiral tungsten 

 filament supported by a molybdenum sleeve. The high potential 

 current propels the electrons to the anode, which acts at the same 

 time as a target. The number of the electrons depends upon the 

 temperature of the filament of the kathode and the velocity on 

 the voltage of the primary current. 



A priori it could be expected that the Coolidge tube would not 

 only produce a greater output of Roentgen rays, but also generate 

 rays of greater penetrating power. Comparative experiments 

 were done with the best model of tubes of the old type and with 

 the Coolidge tube. Both tubes were placed approximately under 

 similar conditions i. e., the same voltage of primary electric current 

 was sent through the coil, the same number of milliampers of high 

 potential current were sent through the tube, and the resulting 

 Roentgen rays showed the same penetrating power. 



To study the distribution of the rays pieces of beef were 



