EATIO OF ELECTROMAGNETIC TO ELECTROSTATIC UNIT 275 



In taking the mean, I have ignored the difference in the weights due 

 to the number of observations, as other errors are so much greater than 

 those due to estimating the swing of the needle incorrectly. 



It will be seen that the series with one discharge is somewhat greater 

 than with a larger number. This may arise from the uncertainty of 

 the correction for the greater number of discharges, and I think it is 

 best to weight them inversely as this number. As the first series has, 

 also, nearly twice the number of any other, I have weighted them as 

 follows : 



Wt. vxlO- 8 



8 298-80 



4 298-48 



3 297-26 



2 297-15 



1 296-69 



Mean 298-15 



Or v = 29815000000 cm. per second. 



It is impossible to estimate the weight of this determination. It is 

 slightly smaller than the velocity of light, but still so near to it that 

 the difference may well be due to errors of experiment. Indeed the 

 difference amounts to a little more than half of one per cent. It is seen 

 that there is a systematic falling off in the value of the ratio. This is 

 the reason of my delaying the publication for ten years. 



Had the correction, A, for the number of discharges been omitted, 

 this difference would have vanished; but the correction seems perfectly 

 certain, and I see no cause for omitting it. Indeed I have failed to find 

 any sufficient cause for this peculiarity which may, after all, be acci- 

 dental. 



As one of the most accurate determinations by the direct method and 

 made with very elaborate apparatus, I think, however, it may possess 

 some interest for the scientific world. 



