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On Interference. We have now to consider another of the phenomena which may occur, when two musical sounds are heard simultaneously; and in the present chapter, we shall suppose the two sounds in question to be simple tones.
Let the horizontal dotted straight lines in fig. 67, represent surfaces of still water; and let two series of waves of equal length
Fig. 67.
and amplitude be, at the same moment, passing from left to right. Let the curved line (1) represent in section the form, that the waves would have, if those of the first series alone were present; and let (2) represent, in the same way, the form, that the water would assume, if the second series of waves alone were passing. Let us also, in the first place, suppose the two series of waves to coincide, so that crest falls on crest, and trough on trough ; that is, let them both be in the same phase, as represented in (1) and (2). Under these circumstances, each series will produce its full effect,