4 Electro-Magnetice Machine. 
and of course their relative energy, may be permanently supported, 
and even carried to an extent much greater than has been hitherto 
attained. 
2. Rotating Machine, composed entirely of electro-magnets, both 
in its fixed and revolving members. 
A machine of this construction has been, this day, March 29, 
1837, exhibited to me by Mr. Thomas Davenport himself, who came 
from New York to New Haven for that purpose. 
It is the same machine that has been already described, except 
that the exterior fixed circle is now composed entirely of electro- 
magnets. 
The entire apparatus is therefore constructed of soft unmagnetic 
iron, which being properly wound with insulated copper wire, is mag- 
netized in an instant, by the power of a very small battery. 
The machine is indeed the identical one used before, except that 
the exterior circle of permanent magnets is removed and in its place 
is arranged a circle of soft iron, divided into two portions to form 
the poles. 
These semicircles are made of hoop iron, one inch in width, and 
one eighth of an inch in thickness. They are wound with copper 
wire insulated by cotton—covering about ten inches in length on each 
semicircle and returning upon itself, by a double winding, so as to 
form two layers of wire, making on both semicircles about one thou- 
sand and five hundred inches. 
The iron was not wound over the entire length, of one of the steel 
semicircles ; but both ends were left projecting, and being turned in- 
ward, were made to conform to the bend of the other 
part, as in the annexed figure, which is intended to VN 
represent one of them; each end that is turned inward 
and not wound is about one third of the length of the semicircle. 
These semicircles being thus fitted up, so as to become, at pleasure, 
galvanic magnets, were placed in the same machine that has been 
already described, and occupied the same place that the permanent 
steel magnets did before. The conducting wires were so arranged, 
that the same current that charged the magnets of the motive wheel, 
charged the stationary ones, placed around it, only one battery being 
used. It should be observed, that the stationary galvanic magnets 
thus substituted for the permanent steel ones, were only about half 
the weight of the steel magnets. This modification of the galvanic 
magnet, is not of course the best form for efficiency ; this was used 
