Elements of natural philosophy (Volume 2-3) . „ . -, -,. 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
Elements of natural philosophy (Volume 2-3) . „ . -, -,. 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 the transmitted orrefracted pulse ; and because A B and A! Bf are respec-tively proportional to A Mand JLiT, this surface is a explanation. ELEMENTS OF ACOUSTICS. 81 • The angle JV7 A D, made bythe normal to the refractedpulse and that to the deviatingsurface, is called the angle ofrefraction. Denote the angleof incidence N A D, which isequal to the angle M A A,Fig. 38, by 9 ; and the angle ofrefraction N A D, which isequal to the angle A A B,Fig. 38, by 9; then will MA = A A sin 9; A B = A A . sin 9;and dividing the first by the second Fig. 39. Refracted sound;
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