PROFESSOR THOMSON ON THE ELECTRO-DYNAMIC QUALITIES OF METALS. 691 
to the wall in an adjoining apartment as near as possible to the middle of the wooden 
cellSj are brought through the partition between the two rooms, and kept always 
ready to be put in communication with the two poles of the battery, however arranged. 
This battery, or parts of it, have been used in nearly all the experiments described 
below in Parts IV. and V., and it has been found very convenient. Some of the wooden 
cells have contained the acidulated solution of sulphate of copper now for more than 
a year [/or more than two years now, Nov. 1856], and as yet their gutta-percha 
linings have shown no signs of injury. 
64. The first of the recent experiments on electrical convection was made with an 
iron conductor prepared as follows : — 
The conductor, XY, consists of two pieces of thin sheet iron 8^ inches long and 
f of an inch broad, and bent so that when put together they form three tubular spaces, 
A, B, C, fig. 6. The iron is cut so as to make prolongations of these tubes of about 
Fig. 6. 
an inch beyond one side of the conductor. The slips thus put together are soldered 
so as to make the tubes perfectly air-tight, one end being closed, and the other left 
open to receive the thermometer-tubes a, h, c, which were cemented air-tight with wax. 
In soldering, great care was taken to prevent the solder from spreading between the 
iron slips. Copper electrodes were now soldered to the ends of the conductor, and 
the junctions were enclosed within pieces of gutta-percha tube, g, h, through which 
a continuous stream of cold water was made to flow. The distance between the 
coolers was 7i inches, and they were placed so that the four spaces between them and 
A, B, C were all equal. Divided scales were attached to the tubes, of which the 
lower ends were immersed in small vessels, k, I, m, containing spirits of wine. The 
conductor between the coolers was wrapped in a large quantity of cotton wool re- 
presented by the space within the dotted line. 
To send a current through the conductor thus prepared, the whole battery, arranged, 
as described below, in two elements, each exposing ten square feet of zinc surface to 
seventeen square feet of copper, was employed : — 
Description and Drawing of Battery with Connexions. 
R, R and S, S, two series of cells, each containing eight porous cells and eight zinc 
plates. 
4 Y 
MDCCCLVI. 
