WITH reference to the letter of Mr. Stanley in NATURE, vol. xxvi. p. 243, I notice the following sentence:—“If we may apply this principle to stringed instruments, we must look rather to the bridge than the transverse motion of the string, as the communicator of the sonorous vibrations which produces the note.” I thought that this was an admitted fact. Upon the shape of the bridge depends the tone of the instrument, as was satisfactorily settled by Stradivari. The bridge is usually made of spotted maple, and its thickness is of the greatest importance, for if it is too thick it will fail to respond to the string vibration. A plain piece of wood as a bridge is absolutely useless, and the tone increases as the proper shape is approximated to.