Elementary Treatise on Natural Philosophy, Volumen4

achromatic analyser angle of incidence beam body bright lines called centimetres centre coincidence colours concave mirror conjugate foci convex convex lens crystal curvature denote diameter direction distance employed equal experiment eye-piece flame focal length frequency of vibration fundamental note glass harmonics Hence Iceland-spar incident ray index of refraction interval inverted law of sines lens lenses luminous point magnifying power medium metres minimum deviation nearly node normal number of vibrations object object-glass oblique observer obtained octave optical ordinary parallel particles pencil perpendicular pipe pitch placed plane mirror plate polarization portion position principal axis principal focus prism produced propagation radius rarefaction ratio reflected rays refrangibility represented retina rotation screen seen side slit solar spectra spectrum spherical string subtends surface telescope tion tone traversing tube undulation velocity of sound vertical vibrations vibrations per second violet virtual image visual angle wave-front wave-length waves