* 
Proceedings of the British Association. 341 
These formule may be expressed in the terms, 
1. The maximum of mechanical effect which may be obtain- 
ed from a machine, ‘is proportional to the square of the number 
of voltaic elements, multiplied into the square of the electro-mo- 
tive force, and divided by the total resistance of the voltaic cir- 
cuit. ‘There enters, moreover, into the formula, a factor which 
[have designated &, and which depends upon the quality of the 
iron, the form and disposition of the rods, and the distance be- 
tween their extremities. The result is, that with reference to 
some other investigations, which 1 have made of voltaic combi- 
nations, and under similar conditions, the use of platinum, zine, 
the resistance being the same, will produce an effect two or 
three times greater than the use of coeppr, zine. 
2. 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 
tods, nor by employing 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, should be con- 
sidered simply as occupying the range of the ordinary mechan- 
isms which serve for the transmission or transformation of the 
velocity, without increasing the available power. So it would 
be possible to use, instead of the ordinary wheelwork, rods of 
greater or less length, or a greater or less quantity of wire, in or- 
der to establish between the force and the velocity the relation 
which the applications to manufacturing processes may require. 
- ‘The mean attraction of the magnetic rods, or the pressure 
Which the machine can exert, is proportional to the square of the 
current. This pressure is indicated by the galvanometer, which 
'n this manner performs the function of the manometer of steam 
engines. 
4 The economic effect, i. e. the duty or the available power, 
divided by the consumption of zinc, is a constant quantity, which 
'S expressed most simply by the relation between the electro-mo- 
lve foree and the factor &, which has been previously noticed. 
Vol. x1, No. 2.—Jan.-March, 1841. 44 
