Oe ae Sit ile aaa 
TRANSACTIONS OF THE SECTIONS. 19 
of the galvanic current, established by Mr. Faraday, it is found that 
the magnetism of malleable iron divided by the consumption of zinc, 
—a quantity which we have called economic effect—is with reference 
to the maximum of this magnetism, a constant, or an expression into 
which neither the thickness of the wire nor the number of the elements 
into which the total given surface of the battery is divided, enters, but 
only the total thickness of the envelope. 
Having finished these first researches, and having obtained these 
results, which were highly satisfactory, not only for their simplicity, 
but also for their practical value, we set about extending our inquiries 
to iron rods of different dimensions. Is there, it may be asked, any 
specific effect produced by the length or thickness of the nucleus ? or 
does the degree of magnetism solely depend upon the construction of 
the helix, and the force of the current? The solution of this new pro- 
blem presents a greater difficulty than the problem which we had suc- 
ceeded in completely solving. Now, we are obliged to take iron rods 
of different dimensions, and consequently, in all probability of different 
qualities. Similar conditions with reference to the action of the electro- 
magnetic helices are likewise difficult to obtain ; and we soon perceived 
that these circumstances rendered it impossible to attain so close an 
accordance as that which we had obtained in our former observations. 
Although these experiments were made two years ago, the results have 
not yet been published, because, being occupied with other labours, 
we have not been able to find the necessary time fur their reduction 
and arrangement, and for the requisite calculations. Nevertheless I 
take the liberty of presenting to the Section some results, which are 
not devoid of interest, and which are intimately connected with the 
question of electro-magnetic machines. We submitted nine cylinders of 
malleable iron, each eight inches in length, and of different diameters, 
from three inches down to one-third of an inch, to the action of a 
voltaic current of the same force in each case, and we obtained the 
amount of magnetic force represented in the following table :— 
Diameter Magnetism Magnetism 
of the rods. observed. calculated. 
3 447 4.42 
QL 378 376 
2 308 310 
1} 246 244 
1 175 178 
$ 158 156 
3 142 135 
3 112 113 
z 87 91 
This calculation has been made according to the formula m = 
131°75 d + 46°75, in which the constants have been obtained by the 
method of the least squares. The differences between calculation and 
observation are not so large that they cannot be attributed to the 
inevitable errors of observation, and to circumstances inherent in the 
c2 
