HANDBOOK OF ACOUSTICS - online book

A complete view of Acoustical Science & its bearings on music, for musicians & music students.

Home | Just The Tune | Order | Contact




ON INTERFERENCE.
139
Fig 70.
will be at rest, as indicated by the uniform shading. Precisely the same thing would occur, if A and B were three or any number of half wave-lengths apart.
Sir John Herschel made use of this principle in the construction of the apparatus shown in fig. 71. The tube of, which should be
Fig. 71.
longer than represented in the figure, divides into two at /, the one branch being carried round m, and the other round n. These two branches again unite at g, to form the tube g p. The U shaped portion n b, which slides air-tight by telescopic joints over the main tube a b, can be drawn out, as shown in the figure. When a vibrating fork is held at o, the sound waves produced, divide at/, and pass along the two branches, reuniting at g, before reaching the ear of the observer at p. Now if the U shaped portion is pushed home to a, the waves through both branches reach the ear together; but if it be gradually pulled out, a point is reached at which the sound disappears altogether. From what has been said above, it