238 Contributions to Electricity and Magnetism. 



121. The most important experiments, in reference to distance, 

 were made in the lecture room of my respected friend Dr. Hare 

 of Philadelphia, with the splendid electrical apparatus described 

 in the Fifth Volume (new series,) of the Transactions of this 

 Society. The battery consists of thirty-two jars, each of the 

 capacity of a gallon. A thick copper wire of about y'^th of an 

 inch in diameter and eighty feet in length, was stretched across 

 the lecture room, and its ends brought to the battery, so as to 

 form a trapezium, the longer side of which was about thirty-five 

 feet. Along this side a wire was stretched of the ordinary bell 

 size, and the extreme ends of 

 this joined by a spiral, similar to 

 the arrangement shown in Fig. 

 13. The two wires were at 

 first placed within the distance 

 of about an inch, and afterwards 

 constantly separated after each 

 discharge of the whole battery 

 through the thick wire. When 

 a break was made in the second 

 wire at a, no magnetism was de- 

 veloped in a needle in the spiral 

 at b, but when the circuit was 

 complete, the needle at each dis- ^ 



charge indicated a current in the ' P'^^^ «^ '^^ ''^''''^' * ^P'"-^^- 

 same direction as that of the battery. When the distance of the 

 two wires was increased to sixteen inches, and the ends of the 

 second wire placed in two glasses of mercury, and a finger of 

 each hand plunged into the metal, a shock was received. The 

 direction of the current was still the same, but the magnetism 

 not as strong as at a less distance. 



122. The second wire was next arranged around the other, so 

 as to enclose it. The magnetism by this arrangement appeared 

 stronger than with the last ; the direction of the current was 

 still the same, and continued thus, until the two wires were at 

 every point separated to the distance of twelve feet, except in 

 one place where they were obliged to be crossed at the distance 

 of seven feet, but here the wires were made to form a right angle 

 with each other, and the effect of the approximation was there- 

 fore (46) considered as nothing. The needle at this surprising 



