hit Hot Platinum in Air at Loiv Pressures. 95 



the production of secondary rays ; but on exposing a wire, 

 which had been made strongly active, to the rays, no diminu- 

 tion of the induced \vi\k was obtained. 



Conclnsion. 



The experiments which have been described show that the 

 positive leak from a hot platinum wire at low pressures is 

 not a definite function of the temperature, but that it gradually 

 decays with time. The complexity of the phenomena seem 

 to indicate that in general tlie ionization is produced by more 

 than one substance ; but where one effect is predominant 

 the rate of decay of the leak is proportional to its value 

 at the time considered. At a constant temperature the 

 induced leak thus falls away as a negative exponential func- 

 tion of the time. 



Further, a wire which has been heated at a given tempera- 

 ture until it has lost the power of discharging positive elec- 

 tricity _, may have that property restored to it by any of three 

 agencies. These are : — (1) Exposure to air ; (2) exposure to 

 the positive discharge from a second hot wire ; and (3) making 

 it an electrode during the passage of a luminous discharge. 



The first and third methods lead to the conclusion that the 

 effect is due to gas. This gas must, however, be in a peculiar 

 state since the experiments show that none of it comes off 

 the wire negatively charged. In the case of the second 

 and third methods the induced activity is much greater 

 when the wire is made the negative electrode. This might 

 indicate that it is due to the positive ions ; but this supposi- 

 tion is rendered untenable by the fact that Rontgen-ray ions 

 produce no effect. The fact that the discharge induces more 

 activity on the negative than on the positive electrode leads 

 to the conclusion that there are more gas molecules in 

 the state necessary to produce the effect in the neighbour- 

 hood of the negative than in that of the positive electrode. 



These effects have been shown to happen between '001 

 and '3 mm. pressure, but there is no reason to believe 

 that similar phenomena would not occur at higher pressures. 



When a '^ revived " wire is heated at a constant tempera- 

 ture the induced activity is gradually dissipated. In every 

 case the activity fell off in such a manner as it would if the 

 rate of decrease were proportional to the activity momen- 

 tarily present. In fact the phenomenon is exactly analogous 

 to a monomolecular chemical reaction. The quantity which 

 corresponds to the velocity of the reaction is probably a 

 function of the pressure of the gas and of the temperature 

 of the wire. 



