i82 Transactions of the Canadian Institute. [vol. ix 



opposite the polonium were symmetrically placed between the poles of 

 a powerful electromagnet. The circular plate held at F could be altered 

 in temperature by liquid air or some other liquid of constant temper- 

 ature in the tube E. The polonium was connected by means of the brass 

 rod B and a screened connecting wire to an electrometer of moderate 

 sensibility. 



III. — Experiments with Carbon at Different Temperatures. 



The method of conducting the experiments was as follows. The 

 carbon plate K was charged to a negative potential of about 80 volts by 

 connecting the outer part of the apparatus to a battery. This high nega- 

 tive potential on the carbon was sufficient to prevent any S rays from 

 leaving the polonium. The Gaede pump was set exhausting the gas from 

 the apparatus and seven minutes after the pump was started the pres- 

 sure of the gas was read by a McLeod Gauge and the rate of charging of 

 the polonium was measured by the electrometer. The charge which 

 came to the polonium was negative and consisted of a current of a rays 

 leaving the polonium, a current of secondary rays coming from the car- 

 bon to the polonium excited by the a ray bombardment on the carbon, 

 and an ionisation current through the remaining gas in the chamber. 

 P.eadings of the charge which accrued on the polonium plate v/ere made 

 at definite intervals of time afterwards until the rate of charging of the 

 plate became fairly constant. This constant value as shewn in the 

 previous paper* was reached when the density of the layer of gas occluded 

 in the surface of the carbon was in equilibrium with the pressure of gas in 

 the vessel, that is, when there was no readjustment going on in the gaseous 

 layer. After the rate of charging of the polonium had become fairly 

 constant a weak magnetic field was established by passing a small current 

 through the electromagnet, and the rate of charging of the polonium was 

 again found. Then larger and larger currents were sent through the 

 electromagnet and readings were taken until the rate of charging of the 

 polonium became constant. This last constant charge which came to 

 the polonium was composed of the a ray current leaving the polonium 

 and the ionisation current through the gas. The magnetic field was used 

 to deflect the slow moving secondary rays coming from the carbon and 

 the constant rate of charging of the polonium denoted that the magnetic 

 field had deflected them all. The influence of the magnetic field in de- 

 flecting the a rays or the ionisation current through the gas was probably 

 very small. Accordingly the difference between the first constant value 

 of the rate of charging of the polonium and the last constant value was a 



*Trans. Canadian Institute, 1912. 

 Phil. Mag. 1912. 



