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66 MAJOR AND MINOR INTERVALS. [II. §33.
intervals. They are expressed in musical notation as follows:—
Minor Third. Major Third. Fourth. 



The reader should endeavour to familiarise himself with these intervals, so that, when he hears the pair of notes which form any one of them successively sounded, he may at once be able to name the interval.
33. The Syren enables us to obtain simple numerical measures of the intervals exhibited on this page.
Let a second circular row, containing sixteen holes, be punched in its disc, and the instrument be set rotating uniformly. If we now blow alternately against the 8hole row and the 16hole row, we shall find that the sound produced at the latter is precisely one Octave higher than the sound produced at the former. If we increase or diminish the velocity of rotation, both sounds will, of course, rise or fall together, but the interval between them will remain unaffected and equal, as before, to an exact Octave. The number of airdischarges corresponding to the more acute sound is, in this case, evidently twice as large in any given time as the number during the 
