Excitement of Galvanic Electricity. 303 
electricity, and thereby occasions the forma- 
tion of hydrogen gas. 
The chemical theory of the Galvanic pile, 
though already suggested in general terms, 
may be considered however, as having been a 
mere outline, till Dr. Bostock undertook to 
give it greater distinctness and consistency.* 
To the extended hypothesis, which he has 
proposed, it is necessary to admit, as a ground 
work, the three following postulates; Istly, 
that the electric fluid is always liberated or 
generated, when a metal or other oxidizable 
substance unites with oxygen; 2dly, that the 
electric fluid has a strong attraction for hydro- 
gen; and 3dly, that when the electric fluid, 
in passing along a chain of conductors, leaves 
an oxidizable substance, to be conveyed 
through water, it combines with hydrogen, 
from which it is again disengaged when it 
returns to the oxidizable conductor. 
To the efficiency of the pile, two circum- 
stances, it is observed by Dr. Bostock, are 
essential ; that the electric fluid be disengaged ; 
and that it be confined and carried forward in 
one direction, so as to be concentrated at the 
end of the apparatus. The first object is ful- 
filled by the oxidizement of the zinc; the 
second, Dr. Bostock supposes, is effected by 
* Nicholson’s Journal 8yo, iii, 9. 
