128 Magneto-Electricity, and Electro-magnetical Machines. 
ducing deflection by magneto-electricity, for it sent the currents 
all in one direction, instead of producing the alternate or vibrating 
motion occasioned by the common magneto-electrical machine. 
It is curious to observe that electro-magnetical engines, moving 
by the reaction of an electro-magnet and a permanent one, are 
also magneto-electrical engines. When electricity is supplied 
to them from a battery, they revolve; and if they be made to re- 
volve by hand or otherwise, they give out electricity ; electricity 
and motion producing each other reciprocally. 
The problem proposed in the first part of this paper, solved by 
the Dipping-needle used as a Magneto-Hlectrical Machine.— 
Does a magneto-electric helix, or coil, act more powerfully by pass- 
ing the poles of the exciting permanent magnet abruptly, by mov- 
ing in a plane perpendicular to that in which the magnet lies, or 
by approaching the pole of the magnet from the middle or neutral 
point, keeping constantly close to the magnet itself? I restored 
the semicircular magnet to its place, still keeping the galvanom- 
eter connected with the instrument. Here, as the coil-bound 
iron needle revolved in the plane of the magnet, and close to it, 
I had one of the conditions proposed in the question. I adjusted 
the torsion index so that it required sixty revolutions of the iron 
needle per minute, to keep the galvanometric needle constantly 
at the point of strongest deflection, viz., parallel to the coils of the 
galvanometer ; then letting it return becols to its place, I found 
the torsion to have been 624°. T'aking out the semicircular 
magnet and placing it in a plane, at right angles to that in which 
the coil-bound iron needle revolved, so that its convex bend pre- 
sented to the west, and its poles only were presented to the iron 
needle at the points of the dip, I obtained the other condition of 
the question, the abrupt production of polarity. 1 then proceeded 
as before, to adjust the torsion index until sixty revolutions per 
minute would evolve electricity enough to hold the galvano- 
metric needle constantly to the point of strongest deflection, and 
letting it return freely to its place found the torsion to have been 
41°. From these experiments, it appears that the deflecting 
power, by abruptly passing the poles, is only about two thirds as 
much as when continuous proximity is preserved. In order to 
determine whether electricity, produced by inversion of polarity; 
is in the simple ratio of the number of inversions in a given time; 
or increases in. some higher power, I varied the above experi- 
