IT has long been known that on all musical instruments of the violin family there is a particular note which is difficult to excite in a satisfactory manner, and that when this “wolf-note”, as it is called, is sounded, the whole body of the instrument vibrates in an unusual degree, and it seems to have been also understood that the difficulty of eliciting a smooth note of this particular pitch is due in some way to the sympathetic resonance of the instrument (Guillemin, œThe Applications of Physical Forces, 1877). In a recent paper (Proc. Camb. Phil. Soc., June, 1915) G. W. White has published some experimental work confirming this view. The most striking effect noticed is the cyclical variation in the intensity of the tone obtained when the instrument is forced to speak at this point. White suggests as an explanation of these fluctuations of intensity that they are due to the beats which accompany the forced vibration imposed on the resonator. The correctness of this suggestion seems open to serious criticism. For the beats which are produced when a periodic force acts on a vibrator are essentially transitory in character, whereas in the present case the fluctuations in intensity are persistent.