434 Note 35: capacity of a circular disk 



In Art. 281 the charge of the globe of 12-1 inches diameter being i, that of 

 a circle 18-5 inches diameter is given as -992. The ratio of the charge of a globe 

 to that of a circle of equal diameter as deduced from this is 1-542. 



In Art. 445 the charge of the globe is compared with that of a pasteboard 

 circle of 19-4 inches diameter. Cavendish gives the actual observations but does 

 not deduce any numerical result from them, which shows that he did not attach 

 much weight to them. As they seem to be the earliest measurements of the 

 kind, I have endeavoured to interpret the observations by assuming that the 

 positive and negative separations were equal when the observations are qualified 

 in the same words by Cavendish. 



I thus find 14-2 or 14-3 for the charge of the globe, and 15-2 for that of 

 the circle, and from these we deduce for the ratio of the charge of a globe to 

 that of a circle of equal diameter 1-5054. 



In Art. 456 the ratio as deduced by Cavendish from the observations on the 

 globe and the tin circle of 18-5 inches diameter is 1-56. 



From the numerical data given in the same article, the ratio would be 1-554. 



Cavendish evidently thought the result given here of some value, for he 

 quotes it in the footnote to Art. 473. 



Another set of observations is recorded in Art. 478, from which we deduce 

 the ratio 1-561. 



It appears by a comparison of Arts. 506 and 581 that Cavendish, at the date 

 of the latter article (which is doubtful), supposed the ratio to be 1-5. (See 

 footnote to Art. 581.) 



At Art. 648 the ratio is stated as 1-54. 



At Art. 654 measures are given from which we deduce 1-542 and 1-37. 



The numbers in Art. 682 are the same as those in Art. 281. 



