1838] WKITINGS OF JOSEPH HENRY. 139 



take place at a less distance than from twelve to fifteen 

 inches, and with a still larger battery and longer conductors, 

 no change was found, although the induction was produced 

 at the distance of several feet. 



120. The facts given in the last paragraph relate to the 

 inductive action of the primary current; but it appears 

 from the results detailed in paragraphs 110 and 114, that the 

 currents of all the other orders also change the direction of 

 the inductive influence with a change of the distance. In 

 these cases however the change always takes place at a very 

 small distance from the conducting wire; and in this re- 

 spect the result is similar to the effect of a primary current 

 from the discharge of a small jar. 



121. The most important experiments, in reference to dis- 

 tance, were made in the lecture room of my respected friend 

 Dr. Hare of Philadelphia, with the splendid electrical appa- 

 ratus 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^Q-th of an inch in diameter and eighty feet in 

 length, w^as 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 sep- 

 arated after each discharge of 

 the whole battery through the 

 thick wire. When a break was 

 madeinthe second wireata, no 

 magnetism was developed in 

 a needle in the spiral at b, but 

 when the circuit was complete, 

 the needle at each discharge 

 indicated a current in the same 

 Fig. 13.-C place of" the battery, b direction as that of the battery, 

 spiral. When the distance of the two 



