282 Dr. G. J. Burch. Some Uses of Cylindrical [Feb. 29, 



organ being connected with the outer coatings of a pair of condensers, 

 the inner coatings of which were connected with the electrometer. 



Fig. 1. 



A full description of the experiment is given in the papers by Gotch 

 and myself, from which this illustration is taken.* 



In order to find the E.M.F. indicated by such a record it is necessary 

 to measure the subtangent — or, in this case, the polar subnormal to 

 the curve at various points according to the method described in my 

 papers on the "Capillary Electrometer."! The method is, however, 

 inapplicable if the angles are too steep. 



It occurred to me that if the ordinates could be diminished and the 

 abscissae magnified by photography the angles might be brought within 

 the measurable range. Accordingly I fixed the original of fig. 1 at 

 56*25 cm. from a photographic plate, with a cylindrical lens of 

 + 12 -5 cm. with its axis horizontal at a distance of 17 -5 cm., and a 

 second with its axis vertical at a distance of 43*75 cm. The result is 

 shown in fig. 2. The definition is remarkably good in the negative, 



Fig. 2. 



* ' Phil. Trans.,' B, vol. 187, p. 347; ' Proc. Koy. Soc.,' vol. 65, p. 434. 

 f ' Phil. Trans.,' A, vol. 183, p. 81 ; ' Proe. Roy. Soc.,' vols. 48, 59, 60, p. 388, 

 and vol. 70, p. 175. 



