158 | PHYSICS, 
insulated no free electricity is observable in the middle of the pile; it 
becomes evident in increasing intensity towards the extremities. If one 
pole be insulated, this alone exhibits free electricity. When both are con- 
nected, a galvanic current is produced. 
The Voltaic pile, as just described, has now gone almost entirely out of 
use, being in many respects very inconvenient and unsuitable. In its stead, 
various other arrangements have been introduced, called cell, trough, cup, 
box, &c., batteries. In a cup battery each pair consists of a plate of zinc and 
copper, connected by a strip of metal. The moistened disks are replaced by 
cups filled with the conducting liquid, and disposed in a circle or straight 
line. Each cup contains the zinc element of one pair and the copper of the 
next. In the trough apparatus ( pl. 20, fig. 52), instead of a series of cups 
there is a rectangular wooden trough, divided into separate divisions or cells 
by transverse partitions. 
Wollaston’s battery, which is shown in pl. 20, fig. 54, from the front, and 
jig. 55, in ground plan, is an illustration of the cup apparatus ; fig. 53 is a 
side view of two pairs of plates. Each vessel contains a zinc and a copper 
plate which do not touch each other ; each zinc plate is connected with the 
copper of the preceding vessel by a strip of copper, or by a wire. cs isa 
strip of copper soldered to the zinc plate, sz, at s; c’s’ is a second strip of 
copper, soldered to a second zinc plate. ‘The copper strip c’s’ is connected 
with a plate of copper which bends round the zinc plate without touching it. 
The same condition obtains with respect to every other zinc plate. All the 
pairs are fastened to a wooden frame, by means of which they may be simul- 
taneously immersed in or raised out of the fluid. 
The tension of Voltaic electricity depends upon the number of elements, 
its quantity upon the size of the plates; we vary our apparatus, therefore, 
accordingly as we require intensity or quantity. A simple quantity series is 
represented in pl. 20, fig. 56. Here c is a vessel formed by two cylinders of 
copper, one within the other. This is filled with acidulated water, and then 
receives the zine cylinder, z, which is kept from contact with the copper by 
pieces of cork. A little cup, b, is attached to both the zinc and the copper 
by a wire, and into it mercury is poured for the sake of securing a continuity 
of circuit when the battery is to be used. 
If a battery of very great surface be required, the calorimeter, an invention 
of the eminent Dr. Hare (pl. 20, fig. 57), may be used to very great 
advantage. This, in a form somewhat different from the original, consists 
of a wooden cylinder about three inches in diameter, and from one to one 
and a half feet high, on which are roiled two pieces of zinc and copper plate, 
separated by strips of cloth, forming a pair of plates from fifty to sixty square 
feet in area. 
In all the batteries hitherto described, the action, although energetic at 
first, rapidly diminishes. This circumstance becomes a great evil when an 
uninterrupted action of long continuance is required, for which reason 
Becquerel and others have invented their constant batteries. Such a battery 
is represented in fig. 58, pl. 20. Here a is a evlinder of thin copper, 
completely closed and coated with sand, b. The bottom, c, is level, the 
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