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.