Direction of gravity. Plumb-line. Relation between the direction of gravity and the surface of still water. Weight. Center of gravity. Experimental study of the motion produced by weight. In vacuum, all bodies fall with the same velocity. Disturbing influence of the air. Inclined plane of Galileo. Atwood’s machine. To prove by experiment; 1º the law of the spaces described; 2º the law of velocities. Morin’s self-registering apparatus with revolving cylinder. Law of the independence of the effect produced by a force upon a body, and the motion anteriorily acquired by this body. Law of the independence of the effects of forces which act simultaneously upon the same body. Experimental demonstration and generalization of these laws. Law of the equality of action and reaction. Mass. Acceleration. For equal masses the forces are as the accelerations which they produce. Relation between the force, mass, and acceleration. Collision. General laws of uniformly accelerated motion. Formulæ. Pendulum. Law of the isochronism of small oscillations and law of the lengths deduced from observation. Method of coincidences or beats. Use of the pendulum as the measure of time. Simple pendulum; formulæ. Compound pendulum: the laws of the oscillations of a compound pendulum are the same as the laws of the oscillations of a simple pendulum whose length may be calculated. Determination by means of the pendulum of the acceleration produced by gravity. This acceleration is independent of the nature of the body. Remark that the formulæ for the motion of oscillation apply to the comparison of forces of any kind, that may be regarded as constant and parallel to themselves in all positions of the oscillating body. Identity of gravity and universal attraction. Measure of weights. Balance. Conditions to be attended to in making it. Absolute sensibility; proportional sensibility. Method of double weighing. Details of the precautions necessary in order to obtain an exact weight. _Different States of Bodies. Hydrostatics._ Solids. Cohesion. Transmission of external pressures. Elasticity. The true laws of elasticity are unknown. Empirical laws in certain simple cases, and for a very small action. Elasticity of compression, extension, torsion. Experimental determination of the co-efficients of elasticity. Limits of elasticity. Limits of tenacity. Ductility. Temper. Cold hammering. Annealing. Liquids. Fluidity. Viscosity. Physical laws which form the basis of hydrostatics:--1º the transmission of external pressures is equal in all directions; 2º the pressure exercised in the interior of a liquid upon an element of a surface is normal to that element, and independent (as to amount) of its direction. These principles are demonstrated by the experimental verification of the consequences drawn from them.