One of our most profound electricians is reported to have exclaimed,
"Give me but an unlimited length of wire, with a small battery, and I
will girdle the universe with a sentence in forty minutes." Yet this is
no vain boast; for so rapid is the transit of the electric current along
the lines of the telegraph wire, that, supposing it were possible to
carry the wires eight times round the earth, it would but occupy _one
second of time_. The immense velocity of electricity makes it impossible
to calculate it by direct observation; it would require to be many
thousands of leagues long before the result could be expressed in the
fractions of a second. Yet Professor Wheatstone devised some apparatus
for this purpose, among which was a double metallic mirror, to which he
gave a velocity of eight hundred revolutions in a second of time. The
Professor concluded, from his experiments with this apparatus, that the
velocity of electricity through a copper wire, one-fifteenth of an inch
thick, exceeds the velocity of light across the planetary spaces; that
it is at least 288,000 miles per second. The Professor adds, that the
light of electricity, in a state of great intensity, does not last the
millionth part of a second; but that the eye is capable of distinctly
perceiving objects which present themselves for this short space of
time.
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