76 



Royal Society. 



Table II. 



Eleclro-raagnet ; 274 yards No. 16 wire. 

 12 cells in series. 



In all the above experiments the cells were charged with I sul- 

 phuric acid +13 water (salt water in the third column) ; and 13-5 

 square inches of surface were immersed. The silver-zinc pairs were 

 1 inch apart, the graphite-zinc, 2 inches. The lifting powers were 

 not read off more closely than to quarter-pounds. The electro-mag- 

 net used in Table I. was a small horse-shoe containing about 10 

 yards of No. 16 wire ; that used in Table II. was one of the electro- 

 magnets used in the construction of the signal bells before described 

 (vide Proc. Roy. Soc, vol. viii. p. 419), and containing 274 yards 

 of No. 16 copper wire. The resistance added in each successive 

 experiment was one bobbin of a similar electro-magnet or 1 37 yards 

 of wire. The resistances in the Table include the resistance of the 

 electro-magnet. The total resistances in Table II. are all multiples 

 of the contents of a single bobbin or 137 yards. A glance from left 

 to right on the same horizontal line shows tlie comparative value of 

 each combination in the several experiments. One or two small 

 irregularities in Table II. in the six-cell results, are doubtless due to 

 the poles of the magnet not having been ground true. 



With respect to durability, the graphite plates in use since 1850 

 are in as good condition as the new ones now in course of manu- 



