186 j Dr. C. Sheard on the Positive 



VII. Increase of Positive Emission produced by previously 

 heating the wire under such conditions as to discharge 

 Negative Electricity. 



In a general way the effects due to heating the wire for a 

 few minutes under —200 yolts and at such temperatures as 

 to give negative currents produced decided increases in the 

 positive currents subsequently obtainable. The decay with 

 time relations of the positive currents at various tempera- 

 tures, following the above mentioned treatment, are almost 

 exactly the duplicates of those portrayed in figs. 4 and 5. 

 This was to be expected, since the expulsion of electrons 

 from the negatively charged atoms would build up positive 

 ions to be subsequently discharged under potential. The 

 ions thus formed would be characteristic of the substances 

 present as impurities in the wire just as shown in figs. 4 

 and 5. Since the latter mentioned effects have been dis- 

 cussed in some detail in this paper, it is deemed sufficient to 

 simply call attention here to the similarity of results in the 

 two modes of treating the wire. 



A sample set of data, chosen from some score or more 

 taken, may be of interest in showing how the positive 

 current-temperature relations are affected by a preceding 

 short-timed negative emission. The first row of figures 

 gives the current values obtainable at various temperatures 

 before heating the wire for 10 minutes at —200 volts and 

 768° C. The negative ionization current was 0*72 div. per 

 sec. The second row gives the positive current readings 

 then obtained. 



Temperature, ° C. 



628 640 654 670 690 714 732 750 765 782 792 810 825 840 



Currents (before 

 negative emis- 

 sion) 



Currents (after 

 negative emis- 

 sion) 



1 09 2-6 62 166 10 15-2 18-2 24 31 43 110 220 



20 5-6 3-8 7-1 16-6 123 14-3 17'5 25 32 46 190 134 185 



It will be noted that the current at 628° C. is increased in 

 the ratio of 20 to 1, and furthermore that this increased current 

 condition falls away to smaller values as the temperatures are 

 raised, indicating clearly that the effect is to be attributed to 

 the production of positive ions under the treatment recorded. 

 As the wire aged, however, and higher temperatures had to 

 be employed before obtaining negative emission, it was found 



