164 DR. FARADAV^S experimental researches in electricity, (series XIII.) 



1648. As long as the terms current and electro-dynamic are used to express those 

 relations of the electric forces in which progression of either fluids or effects are sup- 

 posed to occur (283.), so long will the idea of velocity he associated with them ; 

 and this will, perhaps, be more especially the case if the hypothesis of a fluid or fluids 

 be adopted. 



1 649. Hence has arisen the desire of estimating this velocity either directly or by 

 some effect dependent on it ; and amongst the endeavours to do this correctly, may be 

 mentioned especially those of Dr. Watson* in 1748, and of Professor Wheatstone-}- 

 in 1834 ; the electricity in the early trials being supposed to travel from end to end 

 of the arrangement, but in the later investigations a distinction occasionally appear- 

 ing to be made between the transmission of the effect and of the supposed fluid by 

 the motion of whose particles that effbct is produced. 



1650. Electrolytic action has a remarkable bearing upon this question of the ve- 

 locity of the current, especially as connected with the theory of an electric fluid or 

 fluids. In it there is an evident transfer of power with the transfer of each particle 

 of the anion or cathion present, to the next particles of the cathion or anion ; and as 

 the amount of power is definite, we have in this way a means of localizing as it were 

 the force, identifying it by the particle and dealing it out in successive portions, 

 which leads, I think, to very striking results. 



1651. Suppose, for instance, that water is undergoing decomposition by the powers 

 of a voltaic battery. Each particle of hydrogen as it moves one way, or of oxygen 

 as it moves in the other direction, will transfer a certain amount of electrical force 

 associated with it in the form of chemical affinity (822. 852. 918.) onwards through 

 a distance, which is equal to that through which the particle itself has moved. This 

 transfer will be accompanied by a corresponding movement in the electrical forces 

 throughout every part of the circuit formed (1627. 1634.), and its effects may be 

 estimated, as, for instance, by the heating of a wire (853.) at any particular section of 

 the current however distant. If the water be a cube of an inch in the side, the elec- 

 trodes touching, each by a surface of one square inch, and being an inch apart, then, 

 by the time that a tenth of it, or 25*25 grains, is decomposed, the particles of oxygen 

 and hydrogen throughout the mass may be considered as having moved relatively to 

 each other in opposite directions, to the amount of the tenth of an inch ; i. e. that two 

 particles at first in combination will after the motion be the tenth of an inch apart. 

 Other motions which occur in the fluid will not at all interfere with this result; for 

 they have no power of accelerating or retarding the electric discharge, and possess in 

 fact no relation to it. 



1652. The quantity of electricity in 25*25 grains of water is, according to an esti- 

 mate of the force which I formerly made (861.), equal to above 24 millions of charges 

 of a large Leyden battery ; or it would have kept any length of a platina wire-j-fr of 

 an inch in diameter red hot for an hour and a half (853.). This result, though given 



* Philosophical Transactions, 1748. t Ibid. 1834, p. 583. 



