On the Pitch of Organ-Pipes

In the Philosophical Magazine for June 1877 [Art. 46, vol. I. p. 320] I described some observations which proved that the note of an open organpipe, when blown in the normal manner, was higher in pitch than the natural note of the pipe considered as a resonator. The note of maximum resonance was determined by putting the ear into communication with the interior of the pipe, and estimating the intensity of sounds of varying pitch produced externally.

A more accurate result may be obtained with the method used by Blaikley, in which the external sound remains constant and the adjustment is effected by tuning the resonator to it. About two inches were cut off from the upper end of a two-foot metal organ-pipe, and replaced by an adjustable paper slider. At a moderate distance from the lower end of the pipe a tuning-fork was mounted, and was maintained in regular vibration by the attraction of an electromagnet situated on the further side, into which intermittent currents from an interrupter were passed. Neither the fork nor the magnet were near enough to the end of the pipe to produce any sensible obstruction. By comparison with a standard, the pitch of the fork thus vibrating was found to be 255 of König's scale. The resonance of the pipe was observed from a position not far from the upper end, where but little of the sound of the fork could be heard independently; and the paper slider was adjusted to the position of maximum effect.