THEORY OF GALVANISM. 125 



to admit the two following postulates, that the 

 electric fluid has a strong attraction for hydrogen, 

 and that when in passing through a chain of con- 

 ductors, it leaves the oxidable substance to be con- 

 veyed through water, it combines with the hydro- 

 gen, and is again disengaged from it, whenever it 

 again enters into an oxidable substance. I shall 

 again quote from the essay of the same candid 

 and judicious writer, as his account of the hypo- 

 thesis, although concise, is, at the same time, 

 perfectly correct. 



" To the efficiency of the pile, two circum- Henry's ac- 

 stances are essential ; that the electric fluid should 

 be disengaged, and that it be confined and carried Fig. 5. 

 forward in one direction, so as to be concentrated 

 at the end of the apparatus. The first object is 

 fulfilled by the oxidizement of the zinc ; the se- 

 cond, as Dr. Bostock supposes, is effected by the 

 union of the evolved electricity with nascent hy- 

 drogen, and by the attraction of the next copper- 

 plate for electricity. At the surface of this plate, 

 the hydrogen and electricity are supposed to sepa- 

 rate ; the hydrogen to be disengaged in the state 

 of gas, and the electricity to be conveyed onwards 

 to the next zinc plate. Here, being in some de- 

 gree accumulated, it is extricated in larger quan- 

 tity, and in a more concentrated form, than before. 

 By a repetition of the same train of operations, the 

 electric fluid continues to accumulate in each suc- 

 cessive pair ; until, by a sufficient extension of the 

 arrangement, it may be made to exist at the zinc 



