300 On the Theories of the 
action of the pile suspended by placing it im 
an exhausted receiver, or in any of those gases: 
that are incapable of supporting oxidation? 
Why is its efficiency increased by an atmo- 
sphere of oxygen gas, or by. adding, to the 
water in the cells, several fluids, in a propor- 
tion not sufficient to change materially its 
conducting power? Why is the nitric acid, 
though a worse conductor of ‘electricity than 
the sulphuric, more active m promoting the 
energy of the apparatus? Why is the power 
of these combinations proportional to the dis- 
position of one of the metals composing them 
to be oxidized by the interposed fluid? These 
facts undoubtedly suggest that, in some way 
or other, the chemical agency of the fluids 
employed is essential to the sustained activity 
of the pile. The principle has even been con- 
- ceded by some distinguished electricians, who 
have attempted to explain it in different ways. 
To account for the effect of the interposed 
fluids, Mr. Cuthbertson has suggested a 
theory, which is both ingenious and suffici- 
ently feasible.* With Volta, he assumes: the 
electromotive change in the metals to be the 
first in the order of phenomena. And when 
(he observes) the copper has given, andthe 
* Nicholson’s Journal 8vo. ii. 287. 
