Application to heavy liquids. Free surface, and surface _de niveau_. Pressure upon the parts of the containing vessel, and upon the bottom in particular; hydrostatic paradox; verificatory experiments. Haldat’s apparatus. Hydrostatic press. Application to immersed or floating bodies (principle of Archimedes;) verificatory experiments. (In treating of the equilibrium of floating bodies, the conditions of stability are not gone into.) Superposed liquids. Communicating vessels. Water level. Spirit level; its use in instruments. Densities of solids and liquids. Anemometers. Compressibility of liquids. Piezometer. Correction due to the compressibility of the solid envelop. Gas. Expansibility. Other properties common to liquids and gases. Principle of the equal transmission of pressures in all directions. Weight of gases. Pressure due to weight (principle of Archimedes.) Weight of body in air and in vacuum. Aerostation. Superposed liquids and gases. Communicating vessels. Barometer. Detailed construction of barometer. Barometers of Fortin, Gay-Lussac, Bunten. Indication of the corrections necessary. Mariotte’s law. Regnault’s experiments. Manometer with atmospheric air--with compressed air. Bourdon’s manometer. Law of the mixture of gases. Air pump. Condensing pump. _Primary Notions of Hydrodynamics._ Toricelli’s principle. Mariotte’s vessel and syphon. Uniform flow of liquids. The same of gases. _Molecular Phenomena._ Cohesion of liquids. Adhesion of liquids to solids. Capillary phenomena. Apparent attractions and repulsions of floating bodies. Adhesion of drops. Molecular actions intervene as disturbing forces in the phenomena of the equilibrium and motion of liquids. HEAT. EFFECTS OF HEAT ON BODIES. LESSONS 6-9. _Generalities._ General effects. Arbitrary choice of one of these effects to define the thermometric condition of a body. Conventional adoption of a thermometer. Definition of temperature. _Dilating Effects._ Definition of the co-efficients of linear, superficial, and cubic dilatation. Approximate relation between the numerical values of these three co-efficients. The value of the co-efficient of dilatation depends upon the thermometric substance and the temperature selected as the zero point. It becomes nearly independent of the zero point when the co-efficient is very small. Relation between volume, density, and temperature. Linear dilatation of solid bodies. Ramsden’s instrument. Cubical dilatation of liquids. Dulong and Petit’s experiments on mercury. Discussion. Regnault’s experiments. Cubical dilatation of solids and of other liquids when that of mercury is given. Relations between the volume, density, and elasticity of a gas, and its temperature. Cubical dilatation of gases. Experiments of Gay-Lussac, Rudberg, and M. Regnault. Advantage of varying the methods of experimenting in these delicate researches.