120 An account of the Electro- Magnetic Engine. 



as an established law, that the width of the coils had no influence on 

 the magnetic power, though they were arranged in any of the various 

 positions represented in Figure 1. 



IV. From the experiments which have been made to discover the 

 influence of the number of the coils on the magnetising of the iron, it 

 appeared, that the magnetism was proportional to the number of the 

 coils, so that this law may be thus stated ; — the total effect of the col- 

 lective coils encircling a bar of iron, is equal to the sum of the effects of 

 each single coil. 



The results as to the discovery of the maximum of power which have 

 been established and deduced by algebraic formulas, were as follows : — 

 that the same was independent of the number of plates and thickness of 

 the wires, that, by the due ordering of the battery, we can arrive at the 

 same maximum, be the wire thick or thin ; that, in consequence of the 

 conditions imposed by this arrangement, the number of coils which can 

 be applied is limited ; that the mode of coiling is in practice of no 

 importance, provided that the chain be duly arranged, as the thickness 

 alone is of importance ; that the maximum corresponds with a certain 

 surface of zinc, which cannot be increased; that the maxima of the 

 magnetism are as the square-roots of the zinc-surfaces, and that by 

 increasing the thickness of the coils, the magnetism can only be in- 

 creased to a certain limit. As to the expense and consumption of zinc, 

 Faraday has shewn, that the strength of the current is proportioned 

 to the quantity of zinc dissolved in each canal in a given space of time. 

 This consumption knows no maximum, but increases as regards the 

 effect produced, the thinner the wire is, and in proportion to the 

 fewness of the pairs of plates. As far as the expense and con- 

 sumption of zinc is concerned, when the magnetism is at a maxi- 

 mum, it is wholly indifferent whether that magnetism be attained by 

 means of thin or thick wires, provided only that the number of plates 

 be arranged according to the conditions found on the proper cal- 

 culations. 



The principal result to which all previous experiments have led is, 

 that the iron cylinder being given, we may obtain the same maximum 

 of magnetism, determined by the zinc surface, in innumerable different 

 ways, provided only we adopt the thickness of the wire to the arrange- 

 ment of the chain ; but that the mode in which this maximum is ob- 

 tained, is wholly without influence on the consumption of zinc. 



Jacobi assures Faraday in a letter dated the 21st of June, 1839, that 

 he has succeeded in overcoming the difficulties which the due ordering 

 of the battery presents ; and that, according to his former experiments, 



