536 Royal Society : — 



from the figure, that the current went round the magnet in the same 

 direction as the molecular currents of arrangement (2). 



Experiments were made at intervals of two minutes ; and. on 

 each occasion, the current was allowed to pass through the bridge 

 for ten seconds, the measurement being taken by the first swing 

 of the galvanometer, which lasted for about eight seconds. Three 

 cells of Grove's battery were used for producing this current ; but, 

 on the other hand, six similar cells were employed for magnetizing 

 the electromagnet. The arrangements for magnetizing are not 

 shown in the figure. The distance of the magnet was too great to 

 affect the galvanometer-needle so as to alter its sensibility, the 

 average deflection causing a difference in the zero of about four 

 divisions of the scale. 



2. In the first experiments made, the key at E (see fig.) was not 

 taken out before the magnetism was put on or off, in consequence 

 of which the induction-current, due to the wire coiled round the 

 magnet, affected the galvanometer on these occasions ; but, after 

 December 12th, the key was taken out, so that no induction-current 

 passed. 



The following is a specimen of the observations made : — 



December 17, 1873. 



Time of putting on , . mo1 * Reflection observed Condition of 



current. . (creasing deflection denotes magnet, 



increasing resistance mABC D). 



ll h ll m 312 off 



13 317 off 



15 311 off 



17 .. 345 (1) 



19 328 . . off 



21 306 (1) 



23 303 off 



25 293 (1) 



27 300 off 



29 290 (1) 



31 307 off 



33 ; 283 (1) 



35 292 ,. off 



37 288 (1) 



39 302 off 



41 292 (1) 



43 309 off 



It will be seen from this experiment that the first effect of put- 

 ting on the magnetism was a marked increase of resistance ; but, 

 with this exception, the resistance, when the magnetism was on, 

 was less than the mean of the two resistances on both sides of it, 

 representing the magnetism off. 



3.. The arrangement remained untouched, as far as we know, 

 from December 15, when it was finally made, until December 19, 



