t when a
current of electricity is set in motion, or stopped in a conductor, a
neighboring conductor has a current produced in the opposite direction.
Henry proved that this principle might be made available to produce an
action of a current upon itself, by forming a conductor in the whirls of
a spiral, so that sparks and shocks might be obtained by the use of such
spirals, when connected with a pair of galvanic plates, a current from
which could give no sparks and no shocks. Henry's discoveries of the
effects of a current in producing several alternations in currents in
neighboring conductors--the change of the quality of electricity which
gives shocks to the muscles into that producing heat, and _vice
versa_--his mode of graduating these shocks--his theoretical
investigations into the causes of these alternations--are abstruse, but
admirable; and his papers have been republished throughout Europe. The
heating effects of a galvanic current have been applied by Dr. Hare to
blasting. The accidents which so often happen in quarries may be avoided
by firing the charge from a distance, as the current which heats the
wire, passing through the charge, may be conveyed, without perceptible
diminution, through long distances. A feeble attempt to attribute this
important invention of Dr. Hare to Colonel Pasley, an English engineer,
has been abandoned. This is the marvellous agent by which our eminent
countryman, Morse, encouraged by an appropriation made by Congress,
will, by means of his electric telegraph, soon communicate information
forty miles, from Washington to Baltimore, more rapidly than by
whispering in the ear of a friend sitting near us. A telegraph on a new
plan at that time, invented by Mr. Grout, of Massachusetts, in 1799,
asked a question and received an answer in less than ten minutes through
a distance of ninety miles. The telegraph of Mr. Morse will prove, I
think, superior to all others; and the day is not distant when, by its
aid, we may perhaps ask questions and receive replies across our
continent, from _ocean to ocean_, thus uniting with steam in enlarging
the limits over which our Republic may be safely extended.[2]

Many of our countrymen have contributed to the branch which regards the
action of electrified and magnetic bodies. Lukens's application of
magnetism to steel (called _touching_), the compass of Bissel for
detecting local attraction, of Burt for determining the variation of the
compass, and th