1838] WRITINGS OF JOSEPH HENRY. 115 



29. When the ends of the second coil were rubbed together, 

 a spark was produced at the opening. When the same ends 



cu 



Pig. 8. — a represents coil No. 1, h helix No. 1, and c, (/, handles for receiv- 

 ing the shock. 



were joined by the magnetizing spiral (11), the enclosed 

 needle became strongly magnetic. Also when the secondary 

 current was passed through the wires of the iron horseshoe 

 (12), magnetism was developed; and when the ends of the 

 second coil were attached to a small decomposing apparatus, 

 of the kind which accompanies the magneto-electrical ma- 

 chine, a stream of gas was given off at each pole. The shock 

 however from this coil is very feeble, and can scarcely be 

 felfc above the fingers. 



30. This current has therefore the properties of one of 

 moderate " intensity," but considerable " quantity." 



31. Coil No. 1 remaining as before, a longer coil, formed 

 by uniting Nos. 3, 4, and 5, was substituted for No. 2. With 

 this arrangement, the spark produced when the ends were 

 rubbed together, was not as brilliant as before; the magnet- 

 izing power was much less; decomposition was nearly the 

 same, but the shocks were more powerful, or in other words 

 the " intensity " of the induced current was increased by an 

 increase of the length of the coil, while the "quantity" was 

 apparently decreased. 



32. A compound helix, formed by uniting Nos. 1 and 2, 

 and therefore containing two thousand six hundred and fifty 

 yards of wire, was next placed on coil No. 1. The weight of 

 this helix happened to be precisely the same as that of coil 

 No. 2, and hence the different effects of the same quantity of 

 metal in the two forms of a long and short conductor, could 

 be compared. With this arrangement the magnetizing effects^ 



