TO THE MOVEMENT OF MACHINES. 15 



which I have alluded in Art. 25., support this mode of con- 

 sidering the magnetic state of the inner part of concave surfaces. 

 The electric helix, and this concave surface, are nearly in the same 

 relation as two juxta-posed magnets, with poles of opposite name. 

 There is no manifest effect ; it is merely a disguised magnetic 

 state. 



34. 



The experiments of M. Parrot, which he made only with a bat- 

 tery of small dimensions, led me to think at first that the de- 

 velopment of the magnetism on the inner surface was only very 

 weak, and that, on employing an arrangement sufficiently ener- 

 getic, the magnetization would be shown in a more decided man- 

 ner. This, however, was not the case; for the pile of 16 pairs (30), 

 Avhich sensibly heated the helix, had not the least effect. Notwith- 

 standing this powerful cun-ent, there was still not a trace of mag- 

 netization in a soft iron wire of a millimeter in thickness, which 

 had been connected to the external sm-face of a helix parallel to 

 its axis. On detaching it, and introducing only one of its extre- 

 mities into the interior, and to the centre of the helix, the wire 

 became strongly magnetized. In this experiment, care must be 

 taken not to submit the wire to the influence of the helix, after 

 having completed the circuit ; for the effects of induction which 

 accompany the moments when contact is established or bi'oken, 

 affect the steel (37), and the soft iron made into wire, and which 

 has partly taken the nature of steel. 



35. 



In electro-magnetic experiments, the question as to indefinite 

 currents frequently occurs ; an expression which, in certain cases, 

 should not be employed without modification. In fact, this ex- 

 pression is inexact, for it is especially characteristic of a voltaic 

 current to return to its origin, a condition which must never be 

 lost sight of. Each closed circuit possesses an axis which bears 

 the same relation to electric or magnetic elements, as the axis 

 passing through the centre of gravity does to the mass of the 

 body. These two axes will coincide in symmetrical and homo- 

 geneous circuits. On exposing soft iron to the inductive 

 power of indefinite voltaic cvuTents, we must take into account 

 the position of the electrical axes, so as to be able to predict whe- 

 ther there will be an effect of magnetization or not. A, B, (PI .1. 

 fig. 2.), being any indefinite current, the bar M cannot become 



