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IX. § 96.] ADDITION OF INTERVALS. 189
by the first and third notes, i. e. of the sum of a Fifth and a Major Third ? We will, for shortness, call the three notes (1), (2), (3), in order of ascending pitch.
Our result, then, is the two vibrationnumbers multiplied together. The reasoning is perfectly general, and gives us the following rule.
To find the vibrationfraction of the sum of two intervals, multiply their separate vibrationfractions together.
96. Next, take the opposite case. Let (2) be a Major Third above (1), and (3) a Fifth above (l), and let the vibrationfraction for the interval (2)—(3) be required.

