522 PROF. JACOBI ON THE APPLICATION OF ELECTRO-MAGNETISM 
were always interrupted by some accident, and I think that the action 
would otherwise have lasted still longer. The disengagement of gas 
was very inconsiderable, and took place only at the surface of the nega- 
tive plate. The velocity was always at first from 120 to 122 revolutions 
in a minute, and decreased about half an hour after to 62 revolutions; 
a circumstance which is attributable to the commutator, which had not 
then the present construction. During the rest of the time the motion 
of the apparatus was remarkably uniform, making from 58 to 62 revo- 
lutions in a minute. I must however confess that I have obtained so 
extraordinary an effect only three times. There were always external 
circumstances, dependent upon the form of the voltaic apparatus, which 
counteracted the effect. I might be able to master most of these cir- 
cumstances by constructing a new apparatus, the manipulation of which 
will be more convenient and the effect more certain. 
14. 
We have expressed by A = = the magnetic force of each section of 
“a wire traversed by an electric current. This force is measured by 
the deviation of the needle or by the magnetizing power of the con- 
necting wire. By adopting ‘the law of Faraday we may equally mea- 
sure this current by the disengagement of the gas, which represents at 
the same time the cost of maintaining in action a voltaic apparatus. If 
D be the quantity disengaged, we shall have D a From this it 
follows that recurring to the formule of article 8, the ceconomical 
effect may be expressed by the magnetic power of the whole extent of 
the connecting wire, divided by the development of the gas. This effect 
is inno respect changed either by the enlargement of the surface, or by 
the employment of various branches wound spirally around different bars 
of the same dimension. But by multiplying the helices, and uniting 
them to form 4 continuous wire, the ceconomical effect may be increased 
as much as we please. For the disengagement of the gas, in employ- 
ing 2 helices or 2 units of length, will be expressed by D = aed 
but we may put in action the magnetizing power of the whole ex- 
tent of the conducting wire, and we shall have for the total force 
ssid ; or — n. When the magnetic bars are intended to 
mr+r D 
produce a mechanical motion, the increase of the ceconomical effect 
will reach its limit; since by multiplying the number of the bars, the 
weight of the apparatus and the friction of the pivots in the sockets 
will be at the same time increased, so that that effect can only be ex- 
U 
pressed by — 7 ig Die The maximum of the ceeconomical 
