McClklland and M'Henry— Uncharged Nuclei. 303 



uranium. The difference is probably, however, one of size, as in the initial 

 stages of recovery the particles emitted may not be so large as they become 

 after a prolonged period of rest. 



Nuclei of a different type are emitted at glowing temperatures. In this 

 case the glass does not become fatigued, and the nuclei ai-e probably produced 

 by the decomposition of the glass itself. 



III. 



When platinum wires are heated electrically, nuclei are driven off before 

 the wire begins to glow. This emission lasts only a short time, just as in 

 the case of glass, and is probably due to occluded impurities. 



When these impurities are driven off by lieat, the wire emits no nuclei 

 until it begins to glow. The emission at glowing temperatures is very 

 constant, and does not fatigue. The size and number of the nuclei emitted 

 increase with the temperature. 



Similar results were obtained with a wire of ni-chrome, an alloy of nickel 

 and chromium. 



Thus in all cases examined where nuclei are driven off from a substance 

 by heat an initial emission takes place at low temperatures which falls off 

 rapidly. The emission of nuclei when the substance glows is practically 

 constant. 



SCIENT. PBGC. K.D.S,, VOL. XVI., NO. XXIIT. 2 Q 



