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on aliead_, and give tTiem fitting work to do when they reach 
their destination^ we can prepare the way in any form we 
choose for the coming train. It is well, also, to mention here 
that the electricity employed for this purpose and the wire 
road along which it is destined to travel are such that, 
although it does not attain to Wheatstone^s velocity, it very 
far exceeds the velocity found in the Atlantic cable. It would 
be foreign to the purpose of this article to explain the con- 
ditions under which these differences of velocity arise. It 
would also be out of place — indeed, space will not allow — that 
we should enter into any detailed description of the instru- 
ments or magazines, so to speak, whence the supply of 
electricity is derived for the purpose in question. Voltaic 
electricity is used : we have it as the current form of force. 
The philosophy and construction of many varieties of what is 
called the Voltaic battery will be found in every elementary 
treatise. The particular form employed by myself, and which 
may be taken as a type of this class of apparatus, is the follow- 
ing : — narrow slip of copper is fastened to a plate of zinc, and 
the zinc is cleaned and its surface well saturated with mercury ; 
a plate similar in size is cut from the corrosion or refuse of 
gas retorts, to which also a slip of copper is attached ; the 
surface of this, which we call graphite plate, is covered with a 
coat of fine powder of platinum by an electro-chemical process 
easily carried out, and which is called platinizing. This pair 
of plates are placed (not touching) in a small earthen jar, 
filled or partly filled with vitriol and water — sulphuric acid 
and water — the copper slips being clear of the liquid. In 
practice the plates are six inches by two inches, and the jar 
holds one pint. This simple apparatus thus arranged may be 
said to stand at ease^^ — it is ready day and night at our 
bidding to furnish electricity for at least six months without 
further trouble; then, for at least a further six months, by 
replenishing it with acid water, to replace that consumed 
in action or lost by evaporation ; and then for a third 
and fourth half-year by washing everything and starting 
it afresh in the first instance, and then again replenishing 
it for the liquid lost. By this time the zinc may be found 
to be worn away, and must be replaced; the graphite is 
practically imperishable. This simple apparatus may be 
considered as primed and loaded with electricity, and ready 
to go off at the word of command. The liquid and the plates, 
with their copper slips, are all conductors of electricity ; it can 
travel by them; the dry jar is not. The respective plates 
thus mounted are in a state of electric tension ; the copper 
slip on the graphite plate is ready to give off electricity; the 
copper slip on the zinc plate — I use popular language — is 
