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104 © New Electro-Magnetic and Magneto-E lectric 
Art. X.—A Description of several New Electro-Magnetic and 
Magneto-Electric Instruments and Experiments ; by Josurx 
Hare Aszor, Mem. Am. Acad. Arts and Sciences, &c. 
Tne following articles of apparatus, some of which have been 
invented more than a year, have not hitherto been described in 
any scientific journal. ‘They seem to me to possess important 
advantages over all instruments of a similar kind now in use; 
and, so far as is known to me, some of the results obtained with 
with them are new. They are all manufactured by Mr. Daniel 
Davis, Jr., a very ingenious maker of magnetical instruments of 
this city. 3 
Fig. 1. 
H 
Double Helix and Electrotome.—This instrument is repre 
sented by figure 1. The double helix, a, a, is nine inches long 
and two and a half inches in diameter. It forms a hollow cylit 
der, capable of containing a round rod about three fourths of al 
inch in diameter, and is confined to a base-board by three brass 
bands. The inner helix is composed of five strands of large, 
insulated copper wire, the aggregate length of which is about 
one hundred feet. The similar ends of these strands at one €* 
