MR. DANIELL ON VOLTAIC COMBINATIONS. 
147 
was checked by including in the circuit a cell whose powers had not been exalted by 
the increased temperature which had been communicated to the others. 
At this period of my investigation some unexpected and highly interesting pheno- 
mena occurred, which turned out to be of a very complicated nature, and the un- 
ravelling of which cost me much time and labour. After careful consideration of the 
subject, I have come to the conclusion, that the clearest mode of giving you an ac- 
count of these will be to adhere nearly to the order in which I followed them out. 
In heating the battery in the steamer, it frequently happened (and indeed in the 
very first series of experiments which I made with it) that when the thermometer 
had nearly reached the boiling point, and the action of the battery was at its maxi- 
mum, a sudden cessation would take place ; the decomposition of water in the volta- 
meter, which was proceeding at the rate of 18 or 20 cubic inches per five minutes, 
would stop as suddenly as by the lifting of one of the connecting wires ; and this 
suspension of power would continue for hours, provided the high temperature were 
maintained. Upon turning the steam off, and quickly cooling the steamer, the action 
would return as suddenly as it had ceased, though generally not to the full amount ; 
falling mostly from about 20 cubic inches to 14 or 15. Upon turning the steam on, it 
would again stop, and again be renewed by cooling. Upon closely examining the vol- 
tameter upon these occasions, it was found that the current was not wholly stopped, but 
that there was a small residual action amounting to ^ cubic inch per five minutes. 
These experiments were often repeated with the same general results ; and yet 
there were times when every care had been taken not to vary any of the circumstances 
of the arrangement, when they could not be reproduced. 
In seeking for the cause of these phenomena, there were two which naturally sug- 
gested themselves as probable : the first was the unequal action of heat upon the dif- 
ferent elements of the battery, exciting thermo-electric currents ; and the second the 
possible excitement of opposing currents from the metallic steam case. 
In heating and cooling the battery by the means which I have described, it is ob- 
vious that the temperature of its different parts would be unequally affected ; and, in 
fact, I found by the thermometer that a difference of ten or twenty degrees would 
occasionally exist between the liquid in contact with the zinc and that in contact 
with the copper : these differences I attempted to increase and modify in numberless 
experiments. On one occasion I charged the battery with a cold acid solution of 
sulphate of copper on the outside, and poured boiling standard acid into the interior 
tube : the inequality did not long exist, but its action was steady at 8§ cubic inches 
per five minutes. I heated the connecting wires to different degrees, and ultimately 
placed spirit-lamps under them, to maintain them at a low red heat ; but the 
working rate of the battery, and its steadiness as measured by the voltameter, were 
not sensibly affected thereby. In short, I convinced myself, that though heat was 
obviously connected with the phenomena, heat alone was not their exciting cause. 
With the view of ascertaining whether the residual current, after the sudden cessa- 
u 2 
