l74 DOVE ON THE ELECTRICITY OF INIjUCTION. 



mass of iron by these currents, then with a certain number of 

 spirals we must obtain by means of solid iron a decrease instead 

 of an increase of power. This was directly observed to be 

 the case when five spirals each 400' in length were added to the 

 keeper of the machine ; whilst bundles of iron wire as decidedly 

 increased the action. This phfenomenon is therefore quite iden- 

 tical with that observed for induction by machine electricity*. 



78. When I and II (jo — A + E) are connected, in which case 

 the keeper and the extra spiral are included in the circuit, we 

 obtain phrenomena which are a combination of those observed 

 with the connexion I and III {p — h), and of those with the con- 

 nexion II and III (E). When only one or two empty spirals 

 are inserted, the shocks are very powerful even with a slow re- 

 volution. This great intensity of the shocks renders it difficult 

 to examine the action of inserted iron. Now we have seen at 

 74), that, with the connexion I and III [p — h), when the length 

 of the inserted wire was increased, and particularly when this 

 was in the form of successive spirals, the resulting current was 

 always weaker, and that at last with five spii-als it was almost 

 imperceptible. When therefore j9 — A is nearly equal to zero, then 

 ^— A + E will assume more and more the form of E. But it has 

 been again shown at 77)j that, with the connexion II and III (E) 

 on the insertion of one spiral, solid iron increases the action ; 

 on the contrary, when five spirals were employed, and each con- 

 tained a rod of iron, the action was weakened, whilst bundles of 

 iron wires even in the last case decidedly render the action more 

 powerful. If therefore with the connexion I and II (j9— A + E), 

 and the insertion of one spiral, the increased action of the cur- 

 rent p through E by means of iron is greater than the decreased 

 action of this current j) through A by means of the same iron, 

 we shall obtain eventually an increased action. By the use of 

 many spirals the action of the negative A is more and more in- 

 creased, but then E also comports itself as a negative quantity, 

 as the electrical currents induced in soft iron weaken the physi- 

 ological action of the extra spiral more than the magnetism ex- 

 cited in the iron augments it. The resulting current must therc- 



* It appears to tie not improbable, although I have made no direct experi- 

 ments upon the subject, that similar experiments might be instituted with the 

 extra current of the galvanic battery. With a sufficient number of spirals we 

 ought to obtain, when solid iron is inserted, a weakening action upon the shock 

 on breaking contact; when bundles of iron wires are inserted, an increasing 

 action. 



