Intelligence and Miscellaneous Articles. 229 



magnification on a scale divided into centimetres. Notwithstanding 

 that the images were imperfect, the error of reading was within 

 the tenth of a division. The reading of the distance was made 

 about twenty seconds after the first impulse ; for the leaves were 

 driven beyond the new position of equilibrium, and only attained it 

 after some seconds. It will be seen that this difference of potential 

 measured after twenty seconds, with equally good insulation, is a 

 measure of this magnitude at the time of the impulse. The insu- 

 lation was sufficiently good, for in 100 seconds the deflection sank 

 for instance only from 10*3 to 8*9. In order to test the above 

 formula, one of the poles of one, two, three Daniells was connected 

 with a condenser-plate, the other with the earth and the second 

 movable plate. It is clear that the charge arising from the dif- 

 ference of potential of 1, 2, 3 II Daniells is again a measure for the 

 magnitude P. Hence we have to test the formula ad-\-bd 2 =!P, if d 

 is the deflection determined in double centimetres. The actual 

 distance of the leaves #, expressed in centimetres, is then 2£ : 15. \ 



The condenser consisted of two copper plates, 7 centim. in dia- 

 meter, in which only that screwed on the electroscope was varnished. 

 Each experiment was repeated ten times and the mean taken. 

 Probably owing to the formation of a residue in the shellac, the 

 first deflections were a few percentages too small compared with 

 the later very regular values. 



Measurement gave for B the value 1*91, 5*46, 9*48, corresponding 

 to the value 11 = 1, 2, 3 Daniells. "With the latter two values of 8 

 and El, a=0-438, 6 = 0*0539. In this case the potential-difference 

 corresponding to d = 1*91 represents 1*016 Daniell instead of 

 1 Daniell. 



3=5-13 corresponds to a zinc-carbon element in potassic bichro- 

 mate to which some sulphuric acid was added; hence 11 = 1-914 

 Daniell compared with 1-86 Daniell with the electrometer. 



According to the formula the deflection 17*5 represented this 

 and the three Daniell elements, and thus 11 = 4-914, which measure- 

 ment gave 18*3. The unvarnished copper plate was replaced by a 

 zinc plate of the same size cleaned with emery-paper, the metallic 

 connection established with the condenser, and a deflection of 0*95 

 obtained from two distinct series of observations, each containing 

 ten readings. With 3 = 0-94 the formula gives 



Zn/Cu=0-677 Daniell. 



If (p is the constant ratio between II and P, and if in the above 

 formula S = 15 cc/2 and II = P/0, it passes into the formula 



P = 0V3-825^+3-O32.r 2 , 



which is independent of the magnitude and choice of the condenser. 

 <p was determined by connecting the electroscope with a Beetz's dry 

 pile of 144 elements. Of course the second pile was put to earth. 

 It is quite essential that the resistance of the battery be infinitely 

 small in comparison with the resistance of the insulating parts of 



