What have been described as **periodicities**, such as the daily variations of root-pressure, afford familiar instances of it.

It is mainly because these fisheries are seasonal that the **periodicity** has been noticed, and because of the economic interests involved the study of the seasonal and longer **periodicities** has become very important.

More and more the science seeks to discover **periodicities** and to correlate these with others.

Seasonal **Periodicities** of Life in the Sea.

Suppose now that F =a sin 22rn i t+b sin 21rn 2 t, the second term will evidently produce a series of combination tones of **periodicities** 2n 1, 2772, n, - n2, and n 1 -1-n 2, as in the first method.