130 Magneto-Electricity, and E'lectro-magnetical Machines. 
The above experiments have a bearing on the construction of 
magneto-electrical machines, and may possibly account for the 
effect of those machines, in which the coil is made to revolve at 
the side of the magnet* instead of acting opposite to the ends 
of it. It should be observed, however, that the armature or coil- 
bound keeper, in the common magneto-electric machine, is s0 
short, that it scarcely leaves one pole before it begins to be in 
contact with the next opposite one. Yet it seems to me, that a 
magneto-electrical machine with the keeper revolving within, or 
at the side of, semicircular magnets, joined so as to make a com- 
plete circle, deserves atrial. As the evolution of magneto-elec- 
tricity and the motion of the same instrument used as an electro- 
magnetical machine seem to be in proportion to each other, it 
would appear that the construction adopted by Messrs. Davenport 
and Cooke, in which contiguity is preserved as in my dipping- 
needle, has superior advantages. Whether such machines can 
ever be made to compete with moving powers already in use, OF 
to attaan the maximum effect of electro-magnetism, is an inter- 
5 1 problem. 
Additional Remarks, by Pict. Locke, on # 
by motion, and on motion produced by magnetic pa 
Med. Coll. of Ohio, Feb. 10, 1838. 
TO PROF. SILLIMAN. 
Dear Sir—It gave me great pleasure to receive yours of the 
lst instant. You were pleased to encourage me in the researches 
which I had begun, and I now sit down to communicate to you 
a generalization, which I suggested in my letter of the 28th, in 
which I stated “that electro-magnetical engines, moving by the 
reaction of an electro-magnet, and a permanent one, are also mag- 
neto-electrical engines. When electricity is supplied to them 
from a battery they revolve, and if they be made to revolve, by 
hand or otherwise, they give out electricity ; electricity and mo- 
tion producing each other reciprocally.” I have since e 
* As in those made by Mr. Clarke, of London, and figured in the last number 
