and on a peculiar Condition of Magneto-electric Induction, 353 



which the moment before or after would give a large spark 

 with a wire of the same diameter and 114 feet long. Again, 

 12 inches in length of wire ^th of an inch in diameter gave a 

 much smaller spark than 36 feet of the same wire. 



In both these cases, though the long wires gave the larger 

 spark, yet it was the short wires which conducted the greatest 

 quantity of electricity in a given time ; and that was very evi- 

 dent in the one of small diameter, for the short length be- 

 came quite hot from the quantity of electricity passing through 

 it, whereas the larger wire remained cold. Still there can be 

 no doubt that the sparks from the long wires were of greater 

 intensity than those from the short wires, for they passed over 

 a greater interval of air ; and so the paradoxical result comes 

 forth, that currents of electricity having the same common 

 source, and passing the same quantity of electricity in the 

 same time, can produce in this way sparks of very different 

 intensity. 



This effect, with regard to lengthened wires, might be ex- 

 plained by assuming a species of momentum as being acquired 

 by the electricity during its passage through the lengthened 

 conductor, and it was this idea of momentum which guided 

 Signori Nobili and Antinori in their process for obtaining 

 the magneto-electric spark by means of a common magnet. 

 Whether a current of electricity be considered as depending 

 upon the motion of a fluid of electricity or the passing of 

 mere vibrations, still the essentml idea of momentum might 

 with] propriety be retained. But it is evident that the similar 

 effect produced by the soft iron of increasing the intensity of 

 the spark cannot be explained in this way, i. e. by momentum ; 

 and as it does not seem likely that the effects, which in these 

 cases are identical, should have two causes, I believe that both 

 are produced in the same way, although the means employed 

 are apparently so different. 



When the electric current passes through a wire, that wire 

 becomes magnetic; and although the direction of the mag- 

 netism is peculiar, and very different to that of the soft iron 

 placed in the helix of the first experiments, yet the direction 

 of the magnetic curves, both of the wire so magnetized and of 

 the soft iron magnet, in relation to the course which the cur- 

 rent is pursuing (i. e. in the conducting wire), is the same. If, 

 therefore, we refer the increased spark to a peculiar effect of 

 induction exerted by the magnetism over the passing electric 

 current, all becomes consistent. Let us, for instance, for the 

 sake of reference, represent the magnetism by the magnetic 

 curves : then, in die first place, the longer the wire the greater 



Third Series. Vol.5. No. 29. Nov. 1834. 2 Z 



