Experiments in Electro-Magnetesm. 119 
been effected than what appeared in an instrument before me at that 
time, viz. Ritchie’s revolving galvanic magnet, which consists of a 
horizontal bar of soft iron covered with copper wire, the ends of the 
wire descending into mercury cells. This instrument was the basis 
of my pursuit. Finding that this bar never attained its maximum 
velocity, from the occasional union of the battery poles, I soon reme- 
died this defect by a contrivance, wherein the bar moved vertically, 
and the mercury cells were entirely independent of each other. The 
instrument thus improved became an interesting and useful piece 
of apparatus, and is in fact the revolving interruptor described and 
figured in the last No. of the Journal. ‘The stationary magnets, 
instead of being single contrary poles, at opposite sides of the circle 
described by the bar, were multiplied so as to form an entire circle 
of poles, with the exception of an inch on each side between the 
opposite poles. ‘The magnets were short bars arranged in the form 
of acylinder, somewhat like the staves of a barrel, and the poles 
not in use were united by armatures of soft iron. ‘The velocity of 
this model was very great, but I found the scattering and oxidation 
of the mercury a great inconvenience and soon substituted for it solid 
conductors. ‘The wires on the bar had their similar ends united by 
single wires, which were brought down and soldered by cylindrical 
segments of metal, firmly fixed upon, but insulated from the axis. 
These segments, representing the ends of the wires covering the re- 
volving bars, were insulated from each other by pieces of horn or 
ivory. ‘Two wires connected with the poles of the battery pressing 
against these segments with a spring, furnished sufficient metallic 
contact to ensure the passage of the galvanic current through the 
wires from end to end. As the segments revolved, they presented 
opposite ends of the wires to the fixed battery wires and thus the 
poles were changed.* But the most important discovery in relation 
to the application of this power, is the following, viz. the admissi- 
bility of oil between the solid conducting surfaces. After the ma- 
* Before the appearance of the April No. of this Journal, in which Davenport’s 
machine was partly described, I addressed a letter to Prof. Silliman, to learn if he 
was aware of any experiments of the kind hitherto made. His answer was, ‘‘the 
best information you can have on this subject, will be embodied in the coming No. 
of the Journal.” The Journal appeared ‘with a description of Davenport’s ma- 
chine, but the mode of making battery connection and changing poles was reserv- 
ed, and until within a short time since, [ supposed that mercury was the medium. 
Finding lately that he used dragging wires upon semizones of metal, I have se- 
cured the above arrangement to myself by patent. 
