304 



Miscellaneous. 



power or mechanical effect, the expression T = R v. Let n be the 

 number of the coils of the helix which covers the rods ; z, the number 

 of the plates of the battery ; B, the total resistance of the galvanic 

 circuit ; E, the electro-motive force ; k, a co-efficient, which depends on 

 the arrangement of the bars, the distance of the poles, and the quality 

 of the iron ; we have then for the maximum of the mechanical effect 

 which will be obtained, the expression—- 



I. T 



m iBk 



For the velocity, which corresponds to this maximum, 

 For the resistance acting upon the machine, 



lit a 



4 B 2 



Lastly, for the economic effect, i. e. the duty or the mechanical effect 

 divided by the consumption of zinc in a given time,— 



" These formulae may be expressed in the terms : — 

 " 1st. The maximum of mechanical effect which may be obtained from a 

 machine, is proportional to the square of the number of voltaic elements, 

 multiplied by the square of the electro-motive force, and divided by the 

 total resistance of the voltaic circuit. There enters, moreover, into the 

 formula, a factor, which I have designated k, and which depends upon 

 the quality of the iron, the form and disposition of the rods, and the dis- 

 tance between their extremities. The result is, that with reference to 

 some other investigations, which I have made of voltaic combinations, 

 and under similar conditions, the use of platinum, zinc, the resistance 

 being the same, will produce an effect two or three times greater than the 

 use of copper, zinc. 



" 2nd. Neither the number of the coils of the helix which covers the 

 rods, nor the diameter or the length of the rods themselves, has any 

 influence upon the maximum of the power. It results, therefore, that 

 neither by adding to the length or diameter of the rods, nor by em- 

 ploying a greater quantity of wire, can the power be increased. There 

 is, however, this remarkable fact, that the number of coils disappears 

 from the formula, simply because the force of the machine is in a direct 

 ratio, and the velocity is in an inverse ratio, to the square of this 

 number. It is thus that the number of coils, the dimensions of the 

 rods, and the other constituent parts of an electro-magnetic machine, 



