104 New Electro-Magnetic and Magfieto-E lectric 



Art. X. — A Description of several New Electro-Magnetic and 

 Magneto-Electric Instruments and Experiments ; by Joseph 

 Hale Abbot, Mem. Am. Acad. Arts and Sciences, &c. 



The 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. 



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 cylin- 

 der, capable of containing a round rod about three fourths of an 

 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 ex- 



