190 Miscellanies. 
Mr. Isaiah Lukens, Mr. S. V. Merrick, Mr. E. Hazard, and other _ 
scientific and personal friends whom I met in society on occasion of 
a visit to that city at the period above referred to, were cognizant 
of my experiments and objects many months previous to the public 
announcement of results of a similar kind from any other experi- 
menter. The field of investigation is large, and°as yet not much 
explored, and Mr. Davenport may rest assured, should this notice 
chance to meet his eye, that no one will rejoice more sincerely than 
I shall to hear of his onward progress, while I myself hope also to 
advance in the march of improvement. 
3. Electro-Magnetic Apparatus and Experiments ; by Cuar.es 
G. Pacs, M.D. 
Salem, (Mass.) Aug. 23, 1837. 
TO PROFESSOR SILLIMAN. 
Dear Sir—Since my last communication, I have completed the 
following pieces of electro-magnetic apparatus, for exhibiting the ro- 
tation of conductors by magnets, without the use of mercury. ‘The 
motory force in such experiments is very feeble, but by the use of 
solid conductors, as in figures 1 and 2, I attain a more rapid move- 
ment than when the wires run in mercury. ‘The discovery alluded 
to in the article on the electro-magnetic engine, viz. the admissibili- 
ty of oil between conducting surfaces, I conceive to be of great im-. 
portance, and will doubtless soon change the whole aspect of electro- 
magnetic and dynamic apparatus. It supersedes the use of mercury, 
where freedom of motion and the constant passage of the galvanic 
current are required. 
Fig. 1, represents the ring of De la Rive, iocmed for rotation 
between the poles of a horse-shoe magnet. ‘The ring a, is four 
inches in diameter, and consists of eight turns of copper wire, cov- 
ered with cotton. Its two ends are brought down at 6,6, and sol- 
dered to cylindrical segments of silver. These segments are secured 
upon, but insulated from the axis. Both are to be reduced in size 
as much as is consistent with strength, in order to diminish friction. 
The two conducting wires, connected with a pair of plates by the 
mercury cups on the stand, are bent into a spiral at c and d, in order 
to press them with a slight spring against the segments 6,6. Where 
the instrument is used, a drop of oil is put on the segments. ‘This 
is a pleasing experiment; the ring (if highly colored) revolving so 
