[STEWART] ON EXCITED RADIOACTIVITY 103 
From the numbers given it will be seen that, while on some days 
the positively charged discs gave no indication of excited radioactivity, 
on other days there was clear and distinct evidence that a feeble but 
well marked radioactivity had been excited in them, although they 
were positively charged when exposed. In order to make certain 
that the observed increase in the rate of leak was a true effect and 
not due to the gradual dissipation of a small charge adhering to the 
dises, they were all carefully cleaned and polished before being 
exposed. The increase in the rate of leak, besides, was found to be 
the same, whether the gold leaf was charged positively or negatively. 
Since the above results were obtained the experiments with 
positively charged discs have been occasionally repeated and, although 
in the majority of cases no excited radioactivity has been observed, 
still on several occasions the discs were found to exhibit the same 
feeble activity from exposure. 
As the greatest care was taken to eliminate every chance of error 
in these experiments, it does not seem possible to arrive at any con- 
clusion but the one that under certain circumstances, which as yet are 
unknown, radioactivity can be excited in conductors which are posi- 
tively electrified. ; 
I wish here to express my thanks to Professor J. C. McLennan 
for suggesting the investigation to me, and for his kind supervision 
of the work. 
