concerned in the Phenomena of ordinary Electricity, §c. 203 



25° 45' ; and the needle remained stationary at this degree when 

 the wheel was made to revolve at any greater velocity. Now the 

 sine of 25° 45' is half that of 60°. When the ratio of surface of 

 the brass and wooden teeth was different from that above men- 

 tioned, the results corresponded. M. Pouillet says in conclu- 

 sion, "hence it finally results that the quantity of electricity 

 which constitutes the current is proportionate to the intensity 

 of this current : also the intensity may be taken for the measure 

 of the quantities of electricity*." 



If it be admitted that intensity is the measure of quantity, 

 and that one must be in the direct ratio of the other, it would 

 appear that a " great quantity at a low intensity " cannot exist 

 in a current, always including in the word " current " the di- 

 mensions of the wire in which the electricity flows. The expres- 

 sion seems to imply a contradiction in terms. 



Suppose that the coil of a galvanometer is the surface over 

 which a current is to pass. Each succeeding portion of electri- 

 city can only act by its own quantity, irrespectively of all that is 

 afterwards to follow. It is obvious that the total amount, if it 

 equalled a discharge from the clouds and passed in a long-con- 

 tinued current, has no more influence in deflecting the needle 

 than any small portion of it which may occupy the coil at any 

 particular moment. The efficient quantity can only be the elec- 

 tricity which is then in the coil, without reference to what is to 

 follow, and which, in common cases of its production by metals, 

 may be said not yet to exist, as the zinc intended to evolve it is 

 only in progress of solution. How, then, does the agency of 

 quantity assist in explaining the much more powerful influence 

 of voltaic over frictional electricity in producing deflections ? 

 Quantity can only aid in continuing an effect ; but how was that 

 effect originally produced ? 



If it be proved that the quantity at any one time present in 

 the coil is small, it is also proved that a succession of such small 

 portions, however rapid, can neither increase the effect of those 

 which passed away, nor anticipate the effect of those which are 

 yet to arrive. But it may be said that velocity of successive 

 transmissions may produce accumulation of effect. I reply, that 

 tin- whole catalogue of electro-magnetic phenomena are evidences 

 of the instant cessation of all effect When the cause ceases ; hence 

 there e;in be no accumulation of effects. We find the galvano- 

 meter needle steady during the passage of a Current, provided 

 the chemical action on the voltaic combination continues equable. 



Should it be conceived thai the conducting power of the wire 



constituting the coil is adequate to the transmission of voltaic 



electricity with such rapidity that enormous quantities can pass 



* Pouillet, Elem. de Physique, vol. i. p. 633 et seg. 



