690 PUOFESSOR- THOMSON ON THE ELECTRO-DYNAMIC QUALITIES OF METALS. 
The differences of temperatures here tabulated, and the half sums of the same 
temperatures, are graphically represented in Plate XXXV. The result is obvious, 
either with or without the graphical representation, and affords a striking confirma- 
tion of the conclusion first arrived at by so different an apparatus (§ 31), that the 
Resinous Electricity carries heat with it in iron. 
62. About the same time another form of the experiment was tried on a copper 
tube, with a vessel of oil fitted round it in the middle, and kept hot by a lamp below 
it, and with gutta-percha tubes fitted to conduct streams of cold water round it. 
A current from the battery was sent alternately in the two directions through it, as 
in the previous experiments, and it was attempted to observe the thermal effects by 
means of two open thermometer -tubes with small spherical bulbs, pushed into the 
copper tube from each end, and bent down at right angles outside it, with their lower 
ends immersed in two cups of spirits of wine. The want of any sufficient regulation 
of temperature to keep the liquid column of these air-thermometers within range, 
made it impossible to get any clear indication of a result by this experiment ; but on 
the whole, there appeared to be an effect of the same kind as had been previously 
discovered in copper. 
63. A few weeks ago, I began again to make direct experiments on electrical con- 
vection with a view to obtaining additional evidence in support of the conclusion 
which I had arrived at previously, and to investigate methods by which the nature 
of the quality in other metals could be discovered more readily, and the specific heat 
of electricity in any metal determined in absolute units. I had determined to 
give up the use of the nitric acid battery in consequence of the inconveniences 
which had been alluded to above (§ 34), and accordingly I had constructed a large 
Daniell’s battery; consisting altogether of eight wooden cells lined with gutta 
percha, and fitted with sheet copper, suitably arranged with shelves to bear crystals 
of sulphate of copper ; sixteen porous cells, some of which had served previously 
in the iron battery ; and sixteen zinc plates of the same dimensions as those previously 
used. Each wooden cell had sheet copper not only round its interior, but also a por- 
tion of the same sheet carried across it so as to divide it into two spaces, each com- 
pletely surrounded by the metallic surface. A porous cell is put into each of these 
spaces, and a zinc plate into each porous cell ; the two zincs in the porous cells con- 
tained in the same wooden cell being always united. The ordinary liquids of a 
Daniell’s battery, acidulated solution of sulphate of copper and dilute sulphuric acid, 
are used. The whole battery power thus consists of eight independent cells, which, 
with the connexions in ordinary use, may be arranged either in one or in two elements, 
but which may also, should there be occasion, be readily enough set up in four or in 
eight elements. Any power may of course be used down to the lowest, with only a 
single porous cell and a single zinc plate in one of the wooden cells. The sulphate 
of copper solution is kept constantly in the wooden cells, which remain in a fixed 
position on a shelf. Electrodes from the large commutator (§ 27), which is fixed 
