312 Prof. B. Stewart and Dr. A. Schuster [May 7, 



seconds, the measurement being taken by the first swing of the galva- 

 nometer, 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. 



It will be seen from this experiment that the first effect of putting on 

 the magnetism was a marked increase of resistance ; but, with this excep- 

 tion, the resistance, when the magnetism was on, was less than the mean 

 of the two resistances on both sides of it, representing the mag- 

 netism off. 



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

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

 experiments were interrupted during the Christmas holidays ; and in all 



