Page:Popular Science Monthly Volume 32.djvu/391

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appears another strongly marked period of excess, culminating in 1855, Again, between these three maxima are two lesser extremes, culminating in 1844 and 1868. Thus our curved line marks five periods of maximum rainfall.

Of low extremes we note four, which have their culminations in the years 1839, 1850, 1860, and 1872.

PSM V32 D389 Sun spot curves and lake erie water level 1769 1838.jpg

The intervals between extremes vary from eight to fourteen years, the general mean being eleven years.

Let us now compare with these curves those immediately below, and which represent the periodic changes in the levels of Lake Erie during the half-century.