Eleciro-Magnetic .apparatus. 87 



advantageously employed. A horse shoe magnet would require two 

 such rolls or transverse coils, unless it were bent at right angles near 

 each pole. 



Will you do me the favor to insert this article in the forthcoming 

 number of the American Journal of Science,* and oblige yours 

 respectfully, B. F. Joslin. 



Schenectady, June 25, 1831. 



EXPLANATION OF THE PLATE. 



a The roll composed of silk and copper laminse, turning twelve 

 times round a small hollow cylinder of soft iron, and prevented from 

 uncoiling by the two copper bands or hoops hh. When the copper 

 is exterior to the silk, the bands are made of some imperfectly con- 

 ducting material. 



cc The two projecting extremities of the hollow iron cylinder, 

 which is a small piece of thin gun-barrel. 



dd A brass rod passing through it, and resting at the extremities 

 on the upright columns of the supporting frame. 



ee A brass wire bent horizontally into a semicircular form, for sup- 

 porting the small galvanic element i, composed of two connected cop- 

 per cylinders and an intermediate one of zinc and immersed in a cup 

 of acid 7in, which last is drawn transparent for better illustration. 



ff Two slips of sheet copper, the upper ends of which are solder- 

 ed to the two corners of the outer extremity of the copper sheet, and 

 the lower ends immersed in the mercury of the cup which is soldered 

 to the zinc pole k of the galvanic apparatus. 



gg Similar conductors connecting the copper pole Z with the ex- 

 tremities of the iron cylinder cc, and consequently with the interior 

 extremity of the copper sheet which is soldered to it. 



hh A semicircular bar of soft iron, weighing 1 lb. and having at 

 each end a semicircular notch, adapted accurately to the lower side 

 of the uncovered part of the hollow iron cylinder cc. 



At the middle of this armature or lifter hh, is a hook from which 

 is suspended the 14 lb. weight m. 



One peculiarity of ray electro-magnet apparatus, above described, 

 is the substitution of the roll for the helix. As I stated eight years 

 ago, "it is the transverse or circular and not the spiral directionf 



* The above arrived too late for the last No. (that for July, 1831.) 

 I Alluding to the oblique spiral or helix then employed. 



