McClelland and M'Henry — Uncharged Nuclei. 



301 



of Cj. The numbers show that the emission fell off to zero in about three 

 minutes. 



On increasing the current to 1"0 ampere more nuclei were emitted 

 (although the wire was not glowing). The emission in this case also fell off 

 almost to zero, but took a much longer time than that at "8 amp. The 

 following values of Ca and Ci were got at I'O ampere : — 



It will be seen that the rate of emission gradually decreased, but even 

 after about five minutes was still appreciable. On leaving the current at 

 I'O amp. for thirty minutes, C2 was found to be 15'4 and C, 14'0, so that the 

 emission of nuclei had practically ceased. 



On increasing the current through the wire to 1"2 amperes the wire 

 glowed, .and €2 was 37, while C, was 15-3. The same values were obtained 

 after twenty minutes' heating. 



The initial emission at 0'8 and I'O amperes was not regained by the wire 

 even on being laid aside for over three weeks. It is probably due to the 

 emission of occluded substances in the platinum or to surface impurities 

 received, for example, in handling. A fresh platinum wire which was heated 

 in a Bunsen flame before being examined as above did not emit any nuclei at 

 the temperatures corresponding to O'S and I'O amperes. 



With a wire made of ni-chrome, an alloy of nickel and chromium, results 

 were obtained similar to those described for platinum. The wire in this case 

 began to glow at a current of about 3 amps., but nuclei were emitted from the 

 fresh wire at 1'5 amperes. This initial emission rapidly fell off to zero. 



The emission at glowing temperatures remained constant for hours, but in 

 using one wire from day to day a marked falling-off is observed. This was 



Co 



clearly shown by the values at 4-0 amps, of rf , which fell in about a week 

 from the value 5-4 to 2-5, 1-4, 1-25, and finally 1-2. 



