Self-sustaining Voltaic Battery. 47 
will cause the rate of evaporation to be great or small: thus, 
when the battery is exposed to frequent changes of temperature, 
the loss from the jars will be great, (even though a box is used ) 
if the air can flow in and out. But when the battery can be 
placed in a vault or cellar having a uniform temperature, and not 
subjected to frequent changes of air, then no box will be required, 
if the battery can be filled up every few months. When a vault 
cannot be had, a heap of earth over the box will greatly hinder 
changes of temperature and evaporation. Only let it be remem- 
bered that the jars should be kept full, either by refilling or by 
hindering evaporation. 
The form of a battery described above has advantages over all 
others in simplicity and cheapness, as well as certainty and econ- 
omy of action. Its riddance of the usual appliances for making 
contact, such as binding screws, clamps, and soldered joints, so 
expensive in manufacture, and yet so very uncertain in use, will 
certainly commend it to every one who knows the endless trouble 
which invariably attends.the use of these joinings. How often 
S a lecture been spoiled because there was a bad contact which 
could not be detected; and how often do we hear of a whole 
day being lost in telegraphic operations, from the nitric acid hav- 
ing eaten off the solder which joined a platinum to a zine in the 
Grove’s battery. _Moreover, we have no residues of the zincs— 
no necessity for re-amalgamation. 
To show all the advantages of the arrangements described, 
for maintaining the conditions of voltaic action, would be to take 
a full view of the theory of the generation and diffusion of vol- 
taic electricity, which would be impossible in this communica- 
tion et, to set these advantages in some light, I will take but 
a glance at the voltaic action. 
The universal feature of a voltaic combination is that of three 
substances in a series, in which the two extreme bodies have dis- 
similar properties with respect to the intermediate, which is a 
compound body, so constituted that one of its components can 
be eliminated by one of the extreme bodies, and the other com- 
Ponent by the other extreme body. In all useful batteries, one 
of the extreme bodies is zinc; the other, some less oxydable con- 
tor; and the intermediate, water, or water with some acid, 
Benerally the sulphuric. ‘The relations and actions of these three 
ances will embrace all that relates to the generation of the 
Voltaic current. 
€ will suppose that the function of the zinc is to disturb the 
electrical equilibrinm, by combining with the oxygen of the 
Water, (or, if we consider the electrolyte as sulphate of hydro- 
en, the action will be the same,) that the function of the water 
8 to transmit the disturbance by a wave of decomposition and 
