Relations between Electrical Measurements. 445 



In speaking of a quantity of electricity, we need not conceive 

 it as a separate thing, or entity distinct from ponderable matter, 

 any more than in speaking of sound we conceive it as having a 

 distinct existence. Still it is convenient to speak of the inten- 

 sity or velocity of sound, to avoid tedious circumlocution ; and 

 quite similarly we may speak of electricity, without for a moment 

 imagining that any real electric fluid exists. 



The laws according to which the force described varies, as the 

 shape of the conductors, their combinations, and their distances 

 are varied, have been established by Coulomb, Poisson, Green, 

 W. Thomson, and others. These will be found accurately de- 

 scribed, independently of all hypothesis, in papers by Professor 

 W. Thomson, published in the Cambridge Mathematical Journal, 

 vol. i. p. 75 (1846), and a series of papers in 1848 and 1849. 



15. Meaning of the words iC Electric Current." — When two 

 balls charged by the opposite poles of a battery, with opposite 

 and equal quantities of electricity, are joined by a conductor, 

 they lose in a very short time their peculiar properties, and 

 assume a neutral condition intermediate between the positive and 

 negative states, exhibiting no electrical symptoms whatever, and 

 hence described as unelectrified, or containing no electricity. But 

 during the first moment of their junction, the conductor is found 

 to possess certain new and peculiar properties : any one part of 

 the conductor exerts a force upon any other part of the con- 

 ductor ; it exerts a force on any magnet in the neighbourhood ; 

 and if any part of the conductor be formed by one of those com- 

 pound bodies called electrolytes, a certain portion of this body 

 will be decomposed. These peculiar effects are said to be due to 

 a current of electricity in the conductor. The positive quantity, 

 or excess, is conceived as flowing into the deficiency caused by 

 the negative quantity ; so that the whole combination is reduced 

 to the neutral condition. This neutral condition is similar to 

 that of the earth where the experiment is tried. If the balls are 

 continually recharged by the battery, and discharged or neutral- 

 ized by the wire, a rapid succession of the so-called currents will 

 be sent ; and it is found that the force with which a magnet is 

 deflected by this rapid succession of currents is proportional 

 (cateris paribus) to the quantity of electricity passed through 

 the conductor or neutralized per second ; it is also found that 

 the amount of chemical action, measured by the weights of the 

 bodies decomposed, is proportional to the same quantity. The 

 currents just described are intermittent ; but a wire or conductor, 

 used simply to join the two poles of a battery, acquires perma- 

 nently the same properties as when used to discharge the balls 

 as above with great rapidity ; and the greater the rapidity with 

 which the balls are discharged, the more perfect the similarity of 



