114 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XVII.) 
most extraordinary manner, following- all the contortions of the string of facts (1874. 
1956. 1992.2006.2063.), and yet never showing a case of the production of a current 
by contact alone, i. e. unaccompanied by chemical action. 
2015. On the other hand, how simply does the chemical theory of excitement of 
the current represent the facts : as far as we can yet follow them they go hand in 
hand. Without chemical action, no current ; with the changes of chemical action, 
changes of current ; whilst the influence of the strongest cases of contact, as of silver 
and tin (1997.) with each other, pass for nothing in the result. In further con- 
firmation, the exciting power does not rise, but fall, by the contact of the bodies pro- 
duced, as the chemical actions producing these decay or are exhausted ; the conse- 
quent result being well seen in the effect of the investing fluids produced (1918. 
1953. 1966.). 
2016. Thus, as De la Rive has said, any list of metals in their order should be 
constructed in reference to the exciting fluid selected. Further, a zero point should 
be expressed in the series ; for as the electromotive power may be either at the anode 
or cathode (2040. 2052.), or jointly at both, that substance (if there be one) which is 
absolutely without any exciting action should form the zero point. The following 
may be given, by way of illustration, as the order of a few metals, and other sub- 
stances, in relation to muriatic acid : 
Peroxide of lead, 
Peroxide of manganese, 
Oxide of iron, 
Plumbago, 
Rhodium, 
Platinum, 
Gold, 
Antimony, 
Silver, 
Copper, 
Zinc : 
in which plumbago is the neutral substance ; those in italics are active at the cathode, 
and those in Roman characters at the anode. The upper are of course negative to 
the low T er. To make such lists as complete as they will shortly require to be, num- 
bers expressive of the relative exciting force, counting from the zero point, should 
be attached to each substance. 
vii. Active voltaic circles and batteries without metallic contact. 
2017- There are cases in abundance of electric currents produced by pure chemical 
action, but not one undoubted instance of the production of a current by pure con- 
tact. As I conceive the great question must now be settled by the weight of evi- 
dence, rather than by simple philosophic conclusions (1799.), I purpose adding a few 
