Mr. Spitspury on a Single Galvanic Combination. 79 
quantity of its surface was exposed to the action of the acid 
medium. 
Results, however, were sometimes observed, which scarcely 
coincided with the foregoing law; yet the experiments, in which 
these anomalies were observed, did not appear to have been con- 
ducted in a manner, different from these, in which they were 
absent. This was more particularly the case, where the two 
surfaces of the wires under examination differed not greatly im 
magnitude. It was a considerable time before the cause of this 
anomaly was unravelled ; fortunately it struck us, that the results 
might be materially affected by the position of the surfaces towards 
each other. 
To verify this conjecture, two brass wires were hung so as to 
admit of being placed either parallel to, or across each other; re- 
maining at the same time in contact with the galvanoscope. The 
solution of our difficulties was then immediately apparent. When 
the wires were parallel, or placed in any position, not crossing, 
the greater surface was always positive, as formerly observed: but 
if they were placed across each other, and, at the same time, 
nearly in contact at the point of intersection; then that wire 
which has the greater surface under oxidation at the point of con- 
tact, and above it, is positive; though it have the smaller total 
quantity of surface under action. This law has however a limit; 
when the difference of the two surfaces is very considerable, the 
larger total surface is positive, whether crossed or parallel. 
The diagrams in Plate V. will render these laws clearer, 
where P signifies positive, N negative, the blank space repre- 
senting the oxidating medium. 
In Fig. 1, the wires a, 8 are parallel, the greater surface a is 
therefore positive; but in Fig. 2, though the wire # is less in 
total quantity of surface; yet as by its oblique position, there is 
a greater surface exposed to oxidation at the pomt of contact, 
