86 Electro-Magnetic Apparatus. 
Arr. X.—Electro-Magnetic Apparatus ; by Bensamin F. JOsLIN, 
M. D. Prof. of Nat. Phil. in Union College. 
Proressor Siuuiman.—Sir—In the construction of powerlul 
electro-magnets, the spiral wire, with various modifications, has been 
hitherto universally employed for transmitting the magnetizing agent. 
I have recently taken a different route, with a success equal to my 
expectations. My method consists in applying to a bar of iron a 
single rectangular sheet of copper, of a width nearly equal to the 
length of the bar. The silk is simply laid on the copper and both 
wound simultaneously around the iron, in a direction exactly trans- 
verse. 
A piece of gun barrel eight inches and one fourth in length, about 
three fourths of an inch exterior diameter, and varying in thickness 
from one sixteenth to one eight of an inch, and weighing five ounces 
and one seventh, was covered in this manner with a sheet of copper 
and silk, three feet in length and seven inches and three fourths in 
breadth, leaving one fourth of an inch of each end of the iron ut 
covered for the application of the extremities of a semicircular arma 
ture. The barrel was sustained by a brass rod passing through it and 
resting on a frame. ‘The interior and exterior extremities of the 
metallic sheet were connected respectively with the zinc and coppé 
plates of a single galvanic pair of half a square foot each. he 
weight sustained by the magnet was eleven pounds avoirdupols 
After the addition of one foot and a half to the sheet, making four 
feet and one fourth in all, it sustained fifteen pounds, or nearly forty 
seven times its own weight. This, I believe, is several times as much 
as has ever been sustained by a magnet of this size with so short 4 
circuit. The perfect symmetry of the transmitted current, and the 
preservation of this property during the numerous and gradual changes 
which may be readily made in its length, by attaching the wires su“ 
cessively to different parts of this metallic roll, may suggest new meth- 
ods of investigating some of the laws of electro-magnetic action. 
In the above experiment, one of the shorter edges of the recta” 
gular sheet of copper was soldered to the barrel for the convenient? 
of rolling it tight, and one wire connected with each of its four eo” 
ners. In one instance the copper part of the galvanic element and 0 
the roll composed one continued sheet. In this way all wires might 
be dispensed with. Some other laminated metals might probably be 
