the x-Rays by a Battery Current, 133 



<t'-rays in an efficient manner by means of it. This question 

 has been answered in the affirmative, for the rays are pro- 

 duced with the greatest brilliancy; and it is possible to take 

 photographs of the usual subjects which lend themselves to 

 this method of study. The negatives show strong contrasts, 

 and there are traces of the ligaments and the muscles. 



The great advantage of this new method of producing the 

 rays is in the possibility of regulating the current and the 

 difference of potential which is necessary to excite the rays: 

 this is not possible by any of the other methods in present 

 use. When the w-r&y tube is first connected to the battery- 

 terminals no current flows; it is necessary to heat the tube 

 with a Bunsen burner. At a certain critical temperature the 

 tube suddenly lights with a vivid fluorescence, and when the 

 anticathode glows with a cherry-red the rays are given off 

 with great intensity. I employed a distilled- water resistance 

 of approximately four million ohms in direct circuit with the 

 tube. The current, therefore, was not more than three or 

 four milliamperes. It is an interesting spectacle to see the 

 tube glowing in such a brilliant and noiseless fashion. Since 

 such a large resistance was necessary with the use of forty 

 thousand volts, it seemed possible to excite the rays with 

 fewer cells. Indeed, there is no difficulty in producing them 

 brilliantly with twenty thousand cells ; and I see no reason 

 why they cannot be generated by a much smaller number if 

 a suitable tube is employed. 



Since I employed four million ohms in circuit with the 

 ■i'-ray tube, it is evident that there were no electrical oscilla- 

 tions through this circuit. What is needed for the efficient 

 production of the rays is a current in one direction ; a current 

 moreover of sufficient strength to raise the anticathode to a 

 cherry-red. When the anticathode rises to a white heat, the 

 resistance of the tube falls to such a degree, from the gases 

 which are set free from the terminals and the walls of the 

 tube, that the rays are enfeebled. This change of resistance 

 in the tube is a most important phenomenon. It is evidently 

 produced by the outcoming of gases which have been occluded 

 in the metallic terminals and on the glass walls of the tube. 

 Dr. Rollins of Boston has lately described, in the ' Electrical 

 Engineer ' for May, what seems to me a crucial experiment 

 in this connexion. Two Rontgen-ray tubes of the ordinary 

 focus-plane pattern were joined together by a cross connexion 

 which was at right angles to the axes of the tubes. The 

 arrangement thus constituted a double .«-ray tube. This was 

 exhausted to a high degree : the same degree of rarefaction 

 was present in both tubes. One of the tubes was then heated 



