276 



Mr. J. H. T. Roberts on the 



excluded from the vicinity of the wire ; the same precaution 

 prevents the recurrence of the variations described. The 

 curves shown in fig. 2 give an idea of the nature of these 

 variations. Fig. 2 a is for commercial platinum ; fig. 2 b 



Fig. 2 a. 



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for pure platinum. Various other metals were tried, in- 

 cluding palladium, rhodium, iridium, and ruthenium. All 

 these metals were found to give nuclei in air and oxygen, 

 but not (eventually) in a vacuum. 



Relation between Temperature of Wire and Size of Nuclei *. 

 Experiments were made in order to see how the size of 

 the nuclei given out depended upon the temperature, for a 



* It has been shown by G. Owen (Phil. IVIag. 1903) that nuclei are 

 emitted from platinum wires at very low temperatures ; that the size of 

 the nuclei increases with rise of temperature ; that nuclei are not 

 produced in hydrogen below 1000° C. ; and that the nuclei are un- 

 charged. 



