46 



S. J. Plimpton — Recombination of Ions 



The values of t obtained in this way were also checked by 

 means of a chronograph. 



The duration of the flash was obtained as follows : 

 In fig. 3 is shown the induction coil, X-ray tube, and keys 

 S and F as in fig. 1, except that the key F is disconnected 

 entirely from the potential battery system and put in parallel 



Fig. 3. 



with a spark gap Q, which is in series with the secondary of 

 the induction coil and X-ray tube. Q is a brass connector be- 

 tween the two halves of the secondary coil, and connected also 

 to the primary coil for protection to insulation. This brass 

 connector was removed from one binding screw to a distance 

 of 0*5 millimeters. 



Since the connector Q is in series with the X-ray tube, a 

 spark will occur at Q simultaneously with the flash in the tube 

 unless the contacts of the key F are closed or so nearly closed 

 that the discharge takes place at F instead of at Q. If when 

 the discharge occurs the key F is closed or opened to a greater 

 distance, no spark will be seen at F. A spark is seen at F only 

 when the key F is so situated in the path of the pendulum with 

 regard to the key S that the contacts of the key F are separated 

 by a distance less than 0*5 millimeters and greater than mil- 

 limeters during the flash of X-rays. If it opens near the begin- 

 ning of the flash, only a small spark will appear, since the 

 discharge potential has not then attained its maximum so that 

 when the key has opened only a short distance the resistance 

 becomes too great and the spark ceases. On the other hand, 

 if the key F begins to open so near the end of the duration of 

 the discharge that when its contacts have separated only a very 

 small distance the discharge has ceased, then again only a small 

 spark will be observed. By placing the key F at different 



