156 
MR. DANIELL ON VOLTAIC COMBINATIONS. 
of the battery cells were placed upon zinc plates with interposed flannel moistened 
with dilute sulphuric acid ; the copper was thus placed between two generating plates 
of the same metal. When the three were connected together in regular series with 
a galvanometer, the deflection of the needle was 90° E. When a secondary connec- 
tion was made from the zinc rod of each cell in succession through another galvano- 
meter with the zinc plate on which it stood, the deflection occasioned by the extra 
current was 20° W. In this case it must have flowed from the zinc through the elec- 
trolyte in the flannel to the copper ; from the copper through the electrolyte in the 
cell to the zinc rod; and from the zinc rod through the wire back to the zinc plate. 
When the main circuit was broken the extra current changed its direction, and oc- 
casioned a deflection of the needle 20° E. Upon restoring the primary current the 
extra current again returned to its original direction, and so invariably upon many 
successive repetitions of the experiment. 
When the extra connection was made between the copper of the cell and the zinc 
plate, the deflection of the second galvanometer was always 40° W., or opposite to 
the main current, and was not disturbed by any interruption of the latter. 
Being now satisfied that these extra currents were hydro-electric, and dependent 
upon the action of a liquid upon the metal which was brought into association with 
the regular voltaic combination, I examined more carefully the circumstances of the 
arrangement in which I had supposed that I had insulated the cells, and cut them 
off from any such influence by placing them upon thick glass plates. I now ascer- 
tained that the establishment of the extra current was owing to a thin film of moisture 
formed upon the glass, either by the condensation of steam, or slight leakage from 
the cells. At ordinary temperatures no action was thus excited, but when the tem- 
perature of the combination was sufficiently exalted very energetic currents were 
sometimes developed by a quantity of moisture, which might well have escaped or- 
dinary observation. When great care was taken to make the glass plates perfectly 
bright and dry, the extra current was never produced. 
It was now also clear that not only could independent extra currents be established, 
but that different portions of the main battery current could be diverted into this 
secondary path, and thus the occasional decomposition of water in the voltameter by 
the extra current could be accounted for. 
There is one more relation of the battery current, the diverted current and the extra 
current, which it may be worth while to point out when they are all three established 
at the same moment. Let 1, 2, 3 (fig. 8) represent the section of three battery cells, 
all standing upon blocks of wood in iron cases, the sections of which are represented 
by A, B, C, the bottoms of the cases being covered with dilute acid. The main con- 
nect ions of the battery are* made, and the principal current flows from 1 to 3, from 
3 to 2, from 2 to 1. A diverted current may be led off from 1, and may pass in the 
direction abed through the galvanometer G, or sometimes in the opposite direc- 
tion. At the same time an extra current may be established from C, the iron case 
of the cell 3, through the galvanometer G', in the direction e f g h i. 
