Mr. Norman Campbell on Delta Rays. 297 



Table VI. 

 Copper- Aluminium. Aluminium-Silver. 





Cu electrode. 



Al electrode. 



Al electrode. 



Ag Electrode. 



v=l 



1 



2 



3 Z. 



4 



6 



40 



0-272 

 •430 

 •650 

 •751 

 •820 

 •888 

 •947 



1000 



0-193 

 •365 

 •600 

 •731 

 •823 

 •870 

 •949 



1-000 



0224 

 ■374 

 •584 

 •705 

 •785 

 •878 

 •924 



1000 



0-259 

 •421 

 •63S 

 •749 

 •815 

 •894 

 •946 



1-000 



curve, it cannot be clearly decided which of the two branches 

 resembles the aluminium curve more and which the copper ; 

 but in the case of the silver-aluminium curve it is clear that 

 the branch corresponding to the silver electrode resembles 

 more nearly the aluminium curve and vice versa. Hence, the 

 only definite result which can be deduced on such assump- 

 tions is favourable to the hypothesis that the differences 

 between the curves with different metals shown in fig. 3 are 

 due to differences in reflexion and not to differences in 

 emission, a conclusion contrary to that which has been 

 attained in § 14. But the whole subject is so uncertain that 

 it would be unwise to make any definite statement pending 

 the further observations which are about to be undertaken. 



17. Some experiments were made with the object of 

 determining more closely whether the total radiation from 

 different substances was the same, and whether there was 

 anything of the nature of a true delta radiation from the 

 polonium itself over and above the secondary radiation. The 

 apparatus already described was not very well suited for 

 the purpose, partly because it did not permit of the use of 

 the bare polonium disk as one of the electrodes, partly 

 because the use of the screen formed by the hole on 13 

 reduced unnecessarily the amount of the radiation, and partly 

 because it was difficult to take the apparatus to pieces so as 

 to introduce new substances without effecting small changes 

 in the position of the parts. Accordingly, the disk A was 

 replaced by the bare polonium disk, and I) was replaced by 

 a plain cylinder of the material under investigation, the top 

 of which was pirallel to and 2 mm. above the disk. With 

 such an apparatus, the total saturated positive current should 



