42 



BENJ. PIKE S, JR., DESCRIPTIVE CATALOGUE. 



for very elaborate investigations, connected with these in- 

 struments, thus describes the manner of use : a, is the 

 ribbon coil about 100 feet long ; d, a rasp, the end of which 

 communicates with the zinc cylinder of the battery, through 

 the medium of a cup of mercury ; one end of the ribbon is 

 placed permanently in the cup connected with the copper 

 element, and by drawing the other end smartly over the 

 surface of the rasp, a series of brilliant sparks are produced, 

 arid the electrical current through the coil is rapidly broken 

 and renewed. 



Now on placing coil, c, containing about 100 feet of insu- 

 lated copper ribbon, on coil, a, a plate of glass being inter- 

 posed, and sending the electrical current from the battery 

 through a, it was found that as often as the circuit was 

 interrupted, a powerful secondary current was induced in c, 

 and that when the ends of this coil were rubbed together, 

 sparks were produced ; when a small coil of wire enclosing 

 a needle was interposed, the needle became magnetic ; when 

 a small horse-shoe of soft iron, surrounded by a coil of wire, 

 was interposed, magnetism was developed ; when the ends 

 of the coil were attached to a small decomposing apparatus, 

 gas was given off at each pole, and when the body was 

 interposed, a shock, though a feeble one, was experienced. 



Price, $4 to |8.00. 



Fig. 466. 



Flat Wire Coils. (Fig. 467, as above.) These consist 

 of fine insulated copper wire, from 1000 feet and upwards 

 long, wound in the form of a flat spiral, and carefully ce- 



