140 



SCIENCE. 



[N. S. Vol. V. No. 108. 



tion when thus tested by filter and elec- 

 trometer. 



Similar results were obtained with the 

 end of the suction pipe placed so as to 

 touch the floor of the lead cylinder, or the 

 roof, or the sides. Whether the air was 

 pumped away from a place in the cylinder 

 permeated, or from a place not permeated, 

 by the Eontgen rays, it was in all cases 

 found to be negatively electrified. 



The following are some of the results ob- 

 tained on December 16th and 17th. The 

 electrometer was so arranged as to give 140 

 scale divisions per volt. 



Conditions. — Large lead cylinder metal- 

 lically connected with sheath of electrom- 

 eter. Eontgen lamp surrounded by a 

 lead sheath, which latter was also con- 

 nected to electrometer sheath. There was 

 a window in this lamp sheath 2.5 cm. broad 

 and 5 cm. high. This window could be 

 screened by aluminium or by lead. These 

 screens were always connected metallically 

 to sheaths. During all the experiments a 

 Bunsen lamp was kept constantly burning, 

 with its flame about 30 cm. below the 

 Eontgen lamp. 



Results.' — Eontgen lamp in action; air 

 drawn from lowest point of end of lead 

 cylinder next to the E. lamp. 

 December 16, 3.55 p. m. 



— 61 scale divisions in 2 mins. with aluminium screen. 

 — 63 " " " 2 " " no screen. 



— 14 " " " 2 " " lead screen. 



4.20 p. m. Air drawn from point on lower line o£ lead 

 cylinder 26 cms. distant from E. L. end. 

 — 14 scale divisions in 2 mins. with lead screen. 

 — 78 " " " 2 " " no screen. 



— 24 " " " 2 " " lead screen. 



— 83 " " " 2 " " alumin. screen. 



— 13 " " " 2 " " lead screen. 



December 17. 



E. L. acting, and air drawn through filter. 



End of suction pipe kept 

 in axial line of cylinder. 

 10.47 a. m. cms. 



— 44 in 2 mins. with alumin. screen, 68 from E. L. end. 



" " lead " 68 " " 



—28 " " no " 58 " " 



— 24 in 2mins. with no screen, 48 from E. L. end. 



lead 



alumin. 



alumin. 



lead 



lead 



alumin. 



alumin. 



alumin. 



We had previously made experiments 

 with a sheet-iron funnel 1 metre long, 14.5 

 cms. diameter ; and with a glass tube 150 

 cms. long, 3.5 cms. diameter ; and with an 

 aluminium tube 60 cms. long, 4.5 cms. di- 

 ameter. Air was pumped from different 

 parts while the Eontgen rays were shining 

 along the tubes from one end, which was 

 closed by paraffined paper stretched across 

 it. In every case the air was found to be 

 negatively electrified. 



In those earlier experiments the air 

 drawn away was replaced by air coming in 

 from the laboratory at the open end of the 

 tube. We found evidence of disturbance 

 due to electrification of air of the labora- 

 tory by brush discharges from electrodes 

 between the induction coil and Eontgen 

 lamp, and perhaps from circuit-break spark 

 of induction coil. These sources of disturb- 

 ance are eliminated by our later arrange- 

 ment of lead cylinder covered with card- 

 board at both ends, as described above, and 

 air drawn into it from open air outside the 

 laboratory. 



We have also found a verj^ decided elec- 

 trification of air — sometimes negative,some- 

 times positive — when the Eontgen raj'S are 

 directed across a glass tube or an aluminium 

 tube, through which air was drawn from 

 the quadrangle outside the laboratory, to the 

 filter. 



A primary object of our experiments was 

 to test whether air electrified positively or 

 negatively lost its charge by the passage of 

 Eontgen rays through it. We soon ob- 

 tained an affirmative answer to this ques- 

 tion, both for negative and positive elec- 



