58 THE ROYAL SOCIETY OF CANADA 



VII. On the Existence of a Penetrating Radiation Emitted 

 by Polonium. 



In the earlier portion of the paper when dealing with the con- 

 ductivities represented by the curves shewn in Figs. 2, 4 and 5, 

 it was suggested in explanation of the bend in the curves that pos- 

 sibly this effect might be due to a small volume ionisation in the field 

 due to a penetrating radiation from the polonium. That such a vol- 

 ume ionisation did really exist was shewn by means of the apparatus 

 given in Fig. 7 before it was put together for the experiments de- 

 scribed in section VI. 



In place of its being constructed as shewn in the diagram the 

 ebonite plate was not inserted but in its place a sheet of finely meshed 

 gauze was fixed parallel to the two plates GH and MN, and about 

 half-way between them. The edges of this gauze sheet were turned 

 down and soldered to the plate GH. The polonium coated plate was 

 close to the plate GH, and so within the space between it and the 

 gauze. 



The apparatus as constructed in this way was placed in the steel 

 receiver, which was then filled up with air to over 100 atmospheres. 

 The distance between the gauze and the plate PQ was about 3-5 

 millimetres, and as the alpha rays emitted by the polonium could 

 not have a greater range at this high pressure than a fraction of a 

 millimetre it is clear that these rays could not produce any ionisation 

 in the space between the gauze and the plate MN. On applying a 

 potential difference, however, between the gauze and the plate MN, 

 a well-marked, though small current was obtained which reached 

 saturation with a field of about 20 volts, this current was obtained 

 with positive as well as with negative fields, and with both fields its 

 maximum intensity was the same. This result combined with the fact 

 that the mobilities of the ions are exceedingly small at the high pres- 

 sure used would seem to shew that the current had its origin in ioni- 

 sation produced in the space between the gauze and the plate MN 

 by a penetrating radiation from the polonium rather than in ions 

 diffusing through the gauze into this space from the ionized layer 

 close to PQ. The apparatus was not suitable for testing whether 

 this radiatoin was magnetically deflectable or not but in view of the ex- 

 periments of Chadwick* which shew that gamma rays are produced 

 by alpha rays in certain circumstances, the results would seem to point 

 to the existence of gamma rays accompanying the alpha rays from 

 polonium. The probability of this conclusion being correct is in- 



*Chadwick, Phil. Mag. Vol. XXIV, p. 594, 1912. Phil. Mag. Vol. XXV, 

 d. 193, 1913. 



