Means of producing heat or cold; 1, by changes in density; 2, by changes of state. Freezing mixtures. Vaporization of liquids. Condensation of vapors. Steam-boilers. Warming by hot air and hot water. Various problems. Sensations produced by a jet of vapor. Different physical and chemical sources of heat; percussion, friction, chemical combinations, animal heat, natural heat of the globe, solar heat, &c. It will be remarked that mechanical work may become a source of heat, and heat a source of mechanical work. STATICAL ELECTRICITY.--MAGNETISM.--STATICAL ELECTRICITY. LESSONS 25-27. General phenomena. Distinction of bodies into conductors and non-conductors. Distinction of electricity into two kinds. Separation of the two electricities by friction. Hypothesis of electric fluids. Effects of vacuum of gases and vapors of points. Electrical attractions and repulsions. Electrization by influence. Case where the influenced body is already electrized. Sparks; power of points. Electrization by influence preceding the motion of light bodies. Electroscopes. Electrical machines of Van-Marum, Nairne, Armstrong. Condenser. Accumulation of electricity upon its surface. Leyden jar. Batteries. Electrical discharges. Effects of electricity. Condensing electroscope. Electrophorus. Velocity of statical electricity. Atmospherical electricity. Phenomena observed with a serene sky. Electricity of clouds. Storms. Lightning. Thunder. Effects of thunder. Return-shock. Lightning conductor. Different sources of statical electricity. MAGNETISM. LESSONS 28-30. Natural magnets. Action upon iron and steel. Artificial magnets. The attractive action appears as if it were concentrated about the extremities of magnetic bars. First idea of poles. Direction of a magnetized bar under the earth’s action. Reciprocal action of the poles of two magnets. Names given to the poles. Phenomena of influence. Action of a magnet upon a bar of soft iron; upon a bar of steel. Coercive force. Effects of the rupture of a magnetized bar. Theoretical ideas on the constitution of magnets. More precise definition of the poles. Action of the earth upon a magnet. The earth may be considered as a magnet. Its action may be destroyed by means of a magnet suitably placed. Astatic needles. The magnetic action of the earth is equivalent to a _couple_. Three constants define the couple of terrestrial action. Declination. Inclination. Intensity. Measure of the declination; of the inclination. Magnetic metals. Influence of hammering, tempering, &c. Methods of magnetizing. Saturation. Loss of magnetism. Influence of heat. Magnetic lines. Armatures. Magnetization by the earth’s influence. Means of determining the magnetic state of a body. _Measure of Magnetism and Electricity._ LESSONS 31-32.