Elementary Treatise on Natural Philosophy, Part 4

æther angle of incidence beam beats body called centre colours concave mirror conjugate foci convex convex lens corresponding crystal curvature denote density direction displacement distance eclipse elasticity emitted employed equal experiment eye-piece flame focal length fork frequency of vibration fundamental note glass harmonics Iceland-spar incident ray index of refraction interval inverted law of sines lens lenses luminous point magnifying medium minimum deviation musical nearly node normal number of vibrations object object-glass oblique observer obtained octave optical ordinary parallel particles pass pencil perpendicular pipe pitch placed plane mirror plate polarization portion position principal axis principal focus prism produced propagated rarefaction ratio reflected ray represented in Fig rotation screen seen side slit sonorous spectra spectrum spherical string surface telescope tion tone traversing tube tuning-fork undulation unison velocity of sound vibrations per second virtual image visual angle wave-length waves Young's modulus