Page:Popular Science Monthly Volume 32.djvu/395

Rh 2. The years of maximum and minimum levels of Lake Erie, which are given in feet and tenths below the plane of 1838—the maxima and minima in separate columns,

3. The lag, or interval in time at which the periodic changes in the lake follow inversely those of the sun-spots. One column gives the number of years lag of the lake maxima behind the sun-spot minima; the other of the lake minima behind the sun maxima.

4. The sun and lake "periods" In one column are given the number of years between each maximum of sun-spots and the next preceding maximum, and alternately, the number of years between each minimum of spots and the preceding minimum. In the other column are given the like data for the lake periods.

The phenomena which this table makes apparent are: First, that what I have called the sun and lake periods approximate in length, and the means of each are nearly identical—12·3 and 12·6 years. Second, that the sun and lake periods are not synchronous, but that the changes in the lake follow at considerable distance (lag) behind the sun-spot times. Also that the lake maxima lag behind the sun-spot minima less than do the lake minima behind the sun-spot maxima, the means being, respectively, 3·5 and 4·5 years. That is to say, the waters fall less rapidly than they rise, by the mean of a year. We