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 influence. The discussion of this subject forms, the branch of optics, touching physical science on the one side, the most refined, and the highest range of mathematics on the other. Rittenhouse first suggested the true explanation of the experiment, of the apparent conversion of a cameo into an intaglio, when viewed through a compound microscope, and anticipated many years Brewster's theory. Hopkinson wrote well on the experiment made by looking at a street lamp through a slight texture of silk. Joscelyn, of New York, investigated the causes of the irradiation manifested by luminous bodies, as for instance the stars. Of late, photographic experiments have occupied much attention, and Draper has advanced the bold idea, supported by experiment, that the agent in the so-called photography, is not light, nor heat, but an agent differing from any other known principle. Henry has investigated the luminous emanation from lime, calcined with sulphur, and certain other substances, and finds that it differs much from light in some of its qualities.