298 Dr. T. S. Taylor on the Ionization Curve for the 



The polonium was deposited upon the end of a copper 

 plug, and this plug fitted into an iron one B having a small 

 opening about 1 millimetre in diameter and 6 millimetres 

 high over the top of the polonium. This opening gave a 

 small pencil of rays that fell well within the limits of the 

 ionization-chamber. A thin sheet of mica, equivalent to 

 2 millimetres of air, was placed over the polonium so as to 

 prevent any mercury from coming into direct contact with 

 it and the copper plug upon which the polonium was 

 deposited, in case any should condense in the opening above 

 them. The iron plug B containing the polonium was 

 screwed upon the end of a long iron rod 0, 1*5 centimetres 

 in diameter and 100 centimetres long. This rod was turned 

 out carefully so as to be uniform and was fitted snugly into 

 the plale I) as a tight piston. This was made tight by 

 packing wool-asbestos in the conical shaped opening at the 

 lower end of the extension of the plate D, and then turning- 

 down the nut around the piston as shown in the figure. The 

 lower end of the rod C had a screw of 1 millimetre pitch 

 upon it that passed through a nut supported in a framework 

 extending below the plate D. The framework and nut are 

 not shown in the figure. By turning the nut, the rod C and 

 hence the polonium could be moved toward or away from 

 the ionization-chamber. The exact position of the polonium 

 could be determined by reference to a scale parallel to C and 

 the fraction of a turn that the nut had made. About 12 

 centimetres from the top of the glass tube, it was drawn 

 down and a smaller tube of 3 centimetres diameter sealed on. 

 This tube extended to the plate D, making a distance of 70 

 centimetres from the ionization-chamber to the plale D. 

 The glass tube was fastened to the plate D by means of 

 sealing-wax. 



A small electric furnace was constructed and placed around 

 the iron plug B, for the purpose of preventing the con- 

 densation of any mercury vapour upon the mica over the 

 polonium, and also to assist in maintaining a constant tem- 

 perature throughout the tube. The wires leading to this 

 furnace were inserted through two glass tubes that were 

 extended through the plate D. These tubes were fastened so 

 as to be air-tight where they extended through D by sealing 

 them in with wax. The lead wire E was sealed directly 

 through the end of one of these tubes. The other tube, 

 besides having the wire leading to the electric furnace sealed 

 through it, was extended to the open manometer and air-pump 

 as indicated in the figure. 



The entire upper end of the glass tube containing the 



