Elements of natural philosophy (Volume 2-3) . corresponding points of the in-cident and reflected pulses, this tangent surface is a plane. Inci(ient a„dMoreover, since A B is equal to If A\ and the angles reflected pulsesA If A and A! B A are right, the angles If A A! and gj/withBAfr A are equal, and the incident and reflected pulses deviating equal angles with the deviating surface. Any line which is normal to the front surface of a 80 NATURAL PHILOSOPHY. Eay of sound. Angle ofincidence; Angle ofreflexion; These anglesequal. Fig. 37. pulse, is called a ray of sound. The angle N A
Elements of natural philosophy (Volume 2-3) . corresponding points of the in-cident and reflected pulses, this tangent surface is a plane. Inci(ient a„dMoreover, since A B is equal to If A\ and the angles reflected pulsesA If A and A! B A are right, the angles If A A! and gj/withBAfr A are equal, and the incident and reflected pulses deviating equal angles with the deviating surface. Any line which is normal to the front surface of a 80 NATURAL PHILOSOPHY. Eay of sound. Angle ofincidence; Angle ofreflexion; These anglesequal. Fig. 37. pulse, is called a ray of sound. The angle N A D,which the normal to the incident pulse makes with thenormal to the deviating surface, is called the angle ofincidence. The angle BAD, whichthe normal to the reflected pulsemakes with that to the deviatingsurface, is called the angle of re-flexion / and because the anglemade by two planes is equal tothat made by their normals, weconclude from the foregoing, thatin the reflexion of sound, the anglesof incidence and of reflexion Direction of the § 73. The law which determines the course of the re- refractcd pulse „ . -, -,. in . i i • i i i • determined- fracted pulse is equally simple, and is deduced in a man-ner analogous to the preceding. Let A 3f be an inclined element-ary plane pulse, incident upon a de-viating surface E G, at any the interval of time during whichthe point Mis moving from M to A!,the agitation which begins at A willhave reached some spherical surfacewithin the second medium of whichA B is the radius ; and in like man-ner, the agitation which begins atA\ will have reached some sphericalsurface of which A! Br is the radius,by the time the portion of the inci-dent pulse at M\ will have passed on to A; and thesame of intermediate points of primitive disturbance onthe deviating surface between A and A\ the first and construction and ]ast points of incidence. The surface tangent to all thesespherical surfaces will be the front of t
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