PHILOSOPHICAL SOCIETY OF WASHINGTON. 265 



a second glass cylinder similarly provided with helical tin-foil 

 ribbons in suitable connections a tertiary current of induction 

 was obtained, analogous to that derived from galvanism. " Also 

 by the addition in the same way of a third cylinder, a current of 

 the fourth order was developed." 



Similar as these successive inductions from an electrical dis- 

 charge were to those previously observed in the case of the gal- 

 vanic current, they presented one puzzling diflerence in the direc- 

 tions of the currents of the diflureut orders. " These in the 

 experiments with the glass cylinders, instead of exhibiting the 

 alternations of the galvanic currents, were all in the same direc- 

 tion as the discharge from the jar, or in other words they were all 

 plus.'" On substituting for the tinned glass cylinders, well insu- 

 lated copper coils, " alternations were found the same as in the 

 case of galvanism." The only difference apparently between the 

 two arrangements, was that the tin-foil ribbons were separated 

 only by the thin glass of the cylinders, while the copper spiral 

 coils were placed an inch and a half apart. By varied experi. 

 meuts, the direction of the induced currents was found to depend 

 notably on the distance between the conductors ; — the induction 

 ceasing at a certain distance, (according to the amount of the 

 charge and the characters of the conductors,) and the direction 

 of the induced current beyond this critical distance being contrary 

 to that of the primary current.* "With a battery of eight half- 

 gallon jars, and parallel wires about ten feet long, the change in 

 the direction did not take place at a less distance than from 

 twelve to fifteen inches, and with a still larger battery and '.onger 

 conductors, no change was found although the induction was 

 produced at the distance of several feet." With Dr. Hare's bat- 

 tery of 32 gallon jars, and a copper wire about one-tenth of an 

 inch thick and 80 feet long stretched across the lecture-room and 

 back on either side toward the battery, a second wire stretched 



rent induced from mechanical electricity, by a very siniilar experiment. 

 iPoggendorfif's Aiinalen der Physik unci Cliemle, 1«39, No. 5, vol. xlvii. pp. 

 55-7(3.) 



* The variation in the direction of polarization (without reference to 

 induction current.s) appears to have been first noticed by F. Savary, some 

 dozen years before. In an important memoir communicated to the Paris 

 Academy of Sciences .luly 31, 1826, M. Savary announced that "llie 

 direction of the magnetic polarity of small needles exposed to an electric 

 current directed alons a wire stretched longitudinally, varies with the 

 distance of the wire :"— tlie action beinsr found to be periodical with the 

 distance. M. Savary observed tliree periods, and also the tact that the 

 distances of maximum effect and of the nodal zeros " vary with the length 

 and diameter of the wire, and with the intensity of the discharge." He 

 also found that " when a helix is used for magnetizing, the distance at 

 which the needle placed within it is from the conducting wire, is indif- 

 ferent ; but the direction and the degree of magnetization depends on the 

 intensity of the discharge, and on the ratio between the length and size 

 of the wire." (Crewster's Edinburgh Jour. Sti. Oct. 1826, vol. v, p. 369. J 



39 



