Experiments on the communication of vibrating motion in heterogeneous mediums, on the general direction of the vibrating motion communicated.
Intensification of sounds. Interferences. Beats. Different stringed and wind instruments. Means of setting them in vibration.
A few words on the organs of voice and hearing. Incompleteness of our knowledge on this subject.
OPTICS.
Lessons 16–17. Propagation of Light.
Propagation of light in a straight line. Rays of light. Geometrical theory of shadows. Velocity of light. Rœmer’s observations. Laws of intensity of light. Photometers of Bouguer, Rumford. Intensity of oblique rays. Comparison of illuminating powers. Total brightness. Intrinsic brightness.
Reflection.
Reflection of light: its laws. Experimental demonstration. Images formed by one or more plane mirrors. To ascertain if a looking-glass has its two faces parallel.
Spherical mirrors. Foci, formulæ. Discussion. Images by reflection. Measure of the radius of a spherical mirror.