Metals under the Influence of Alpha Bays. 311 



tube, and amber, and the joints made tight with sealing wax. 

 The platinum foil was arranged so that it could be exposed to 

 a pencil of a-rajs from polonium deposited on the end of a 

 copper plug 4 mm in diameter. Between the polonium and the 

 platinum, one could interpose aluminium foils, without inter- 

 fering with the vacuum, in the manner described in the former 

 paper. Two, three, four, five, or six layers of foil could be 

 interposed, each 3 - 2 X 10~ 4em thick. The case was exhausted 

 to about , 0001 mm with the help of charcoal and liquid air ; one 

 of the insulated copper rods which earned the platinum foil 

 was connected with a quadrant electrometer, the case surround- 

 ing the exhausted chamber was charged positively, and meas- 

 urements of the negative current leaving the platinum were 

 taken in the usual manner. After an " ionization curve " had 

 been determined in this way, the platinum strip could be 

 heated by a current sent through it and the two copper rods, 

 and the curve could be again determined, when the liberated 

 gas had been removed. 



Even before the platinum strip was heated its behavior 

 gave evidence that the occluded gases had some effect upon the 

 phenomena, if only a temporary one. With the metals used 

 previously, the saturation value of the current had been 

 obtained with + 40 volts on the case. With the platinum, an 

 hour after the liquid air had been applied to the charcoal, it 

 required + 160 volts to cause saturation and the current at 

 this potential was 20 per cent greater than at 40 volts. Four 

 hours later, 120 volts was sufficient to cause saturation, and the 

 current was only 12 per cent greater than at 40 volts. After 

 an interval of 24 hours, saturation was reached at 80 volts with 

 a 5 per cent increase over 40 volts. During the same time the 

 magnitude of the current (taken under similar conditions) fell 

 off about 30 per cent. But the shape of the ionization curve, 

 obtained by using a saturating potential and interposing 

 aluminium foils, changed very little, if at all, while these very 

 considerable changes were going on in the conditions of satura- 

 tion and in the actual magnitude of the current. The results 

 are given in Table 1. The first line of the table gives the 

 time after the liquid air was applied to the charcoal bulb, the 

 second line gives the value of the currents (with two foils inter- 

 posed) corresponding to these times ; the last five lines of the 

 table give the values of the current when different numbers of 

 foils are interposed, the current with two foils being taken as 

 100 in each case, to facilitate comparison. 



It will be seen that the relative values for 2, 3, and 4 foils 

 show no progressive change with the time ; the differences 

 between them are of the order of magnitude of the experi- 

 mental errors. The values for 5 and 6 foils, however, appear 



