112 ROYAL SOCIETY OF CANADA 



Mach and Rimmer' while investigating the emanation content 

 of the atmosphere at Vienna also made some measurements on the 

 ionisation of air confined in closed metalUc vessels, and from their 

 measurements they were led to conclude that the penetrating radia- 

 tion was more intense in the mornings and in the evenings than at 

 noonday. 



Amongst others Wood and Campbell,^ at Cambridge, England, 

 made an extensive examination of the penetrating radiation for a daily 

 variation. In their experiments they made measurements on the 

 ionisation in different gases contained in closed metallic vessels of 6000 

 cc. capacity, and they used a sensitive quadrant electrometer as the 

 measuring instrument. 



From their experiments they showed that a periodic variation 

 occurred in the ionisation of the enclosed gases having two maxima 

 and two minima each twenty-four hours. They also shewed that the 

 periodic variation was independent of the nature of the enclosed gas, 

 and that the periodicity was independent of the metal of which the 

 enclosing receiver was made. Their ionisation curves representing 

 these periodic changes were found, too, to be approximately the same 

 as the curves representing the variations of atmospheric potential. As 

 to the magnitude of the changes noted, these experimenters found on 

 the average that the variations in the ionisation which took place in 

 any one day amounted to about 12% of the whole. 



McKeon,^ of Washington, U. S. A., made an attempt to study 

 the radiation by examining the variations in the potential assumed 

 by an insulated metal cylinder placed within and completely sur- 

 rounded by a second metalhc cyhnder, 120 cms. long and 20 cms in 

 diameter. In his observations he noted a double daily variation in the 

 potential of the insulated cylinder. The effect measured in his 

 experiments, however, does not appear to be exclusively dependent 

 upon the intensity of the penetrating radiation. 



Strong,^ of Baltimore, also made a study of this penetrating 

 radiation using a small enclosed gold-leaf electroscope as the measuring 

 instrument. In his experiments he observed the loss of charge from 

 this instrument in a variety of places including (1) a room in the 

 Physical Laboratory at Johns Hopkins University, (2) a cistern 

 filled with rain water, the electroscope being placed at the centre, 

 and (3) a room in the open country in the State of Pennsylvania near 

 Mechanicsburg. 



' Phys. Zeit. 7, pp. 617, Sept. 15, 1906. 



- Phil. Mag., Feb. 1907. 



3 Phys. Rev., 1907. 



* Phys. Rev., July, 1908. 



