Intelligence and Miscellaneous Articles. 



397 



point (quantity of electricity on the unit of surface) is proportional 

 to the potential. 



The proportionality between the difference of potential and the 

 intensity is easy to verify by means of the mirror-electrometer which 

 I described in a communication on the 19th of February last. One 

 of the pairs of sectors of the electrometer takes the same potential as 

 A, and a quantity of electricity proportional to that potential ; the 

 other pair takes the same potential as B. 



Between the poles of a pile, liquid or metallic resistances were in- 

 terposed ; Pouillet's tangent-compass gave the intensities for the 

 strong currents, Weber's for the feeble ones. The electrometer 

 measured the differences of potential or tension* corresponding to 

 the extremities of various coils of known lengths of telegraphic 

 wire. The results which follow are referred to a kilometre of wire, 

 equivalent to 100 metres of Pouillet's unit (a column of mercury of 1 

 metre length and 1 millim. section). 



The difference between the two poles of a Daniell's element, open, 

 is represented by 100. 



Electrometer. 



Compass. 



Deflections. 



Ratio of one 

 deflection 

 to the fol- 

 lowing. 



Pouillet's. 



Weber's. 



Ratio be- 

 tween two 

 successive 

 tangents. 



1 turn of 

 wire. 



10 turns. 



146 

 67-6 

 40-34 

 28 

 9-37 

 3-96 

 1-64 



218 



1-680 



1-44 



2-99 



2-366 



2-414 



43 42 (tan =0-956) 



23 15 (tan =0-429) 



14 18 (tan =0-255) 



9 39 (tan =0-17) 







218 



1-677 



1-50 



3 



2-358 



2-383 











63-67 

 2122 

 9 









86-4 

 36-25 





The current being produced by eight fresh Daniell's elements, the 

 number given by the electrometer shows in each case the total re- 

 sistance of the circuit expressed in kilometres. 



It was ?1« in the 



140 



first measurement, ?^ in the second f. 



* This word " tension " is generally employed in the case in which the 

 expression " potential " will be adopted. 



t I suppose here that the electromotive force of a Daniell's element does 

 not change when the current passes. Direct experiments have shown me 

 that it is, except one per cent., the same when the circuit is open and when 

 it is closed with as little external resistance as possible. 



