e could be measured by the observations of small simultaneous
changes in the position of the magnetic needle, led to the knowledge of
the curious fact, that these changes, which had been traced as
simultaneous, or nearly so, in the continent of Europe, did not so
extend across the Atlantic.

Kindred to these two branches are electro-magnetism and
magneto-electricity, connected with which, as discoverers, are our
countrymen Dana, Green, Hare, Henry, Page, Rogers, and Saxton. The
reciprocal machine for producing shocks, invented by Page, and the
powerful galvanic magnet of Henry, are entitled to respectful notice.
This force, it was thought, might be substituted for steam; but no
experiments have as yet established its use, on any important scale, as
a motive power. The fact that an electrical spark could be produced by a
peculiar arrangement of a coil of wire, connected with a magnet, is a
recent discovery; and the first magneto-electric machine capable of
keeping up a continuous current was invented by Saxton.

Electricity and magnetism touch in some points upon heat. Heat produces
electrical currents; electrical currents produce heat. Heat destroys
magnetism. Melted iron is incapable of magnetic influence. Reduction of
temperature in iron so far decreases the force, that a celebrated
philosopher made an elaborate series of experiments to ascertain whether
a great reduction of temperature might not develop magnetic properties
in metals other than iron. This branch of thermo-electricity has
received from us but little attention. Franklin's experiments, by
placing differently colored cloths in the snow, and showing the depth to
which they sank, are still quoted, and great praise has been bestowed
abroad on a more elaborate series of experiments, by a descendant of
his, Dr. A. D. Bache, proving that this law does not hold good as to
heat, unaccompanied by light. The experiments of Saxon and Goddard
demonstrate that solid bodies do slowly evaporate. It is proper here to
mention our countryman, Count Rumford, whose discoveries as to the
nature and properties of heat, improvement in stoves and gunnery, and in
the structure of chimneys and economy of fuel, have been so great and
useful.

Light accompanies heat of a certain temperature. That it acts directly
to increase or decrease magnetic force, is not yet proved; and the
interesting experiments made by Dr. Draper, in Virginia, go to show that
it is without magnetic influe