Page:Elementary Text-book of Physics (Anthony, 1897).djvu/196

tone (§ 156). An exhaustive research by König, however, has demonstrated that beats are perceived when neither of the above suppositions is admissible. Figs. 63 and 64 show that the resultant vibrations are affected by changes of amplitude similar to, though less in extent than, the changes which occur when the tones are nearly in unison. In Fig. 63 I represents a flame image obtained when two tones making $n$ and $n\pm m$ vibrations, respectively, are produced together, and II represents the image when the number