Page:Popular Science Monthly Volume 32.djvu/399

Rh 3. That the times of maximum and minimum rainfall occur inversely as the temperature, and follow after, with mean intervals of one to four years,

4. That the times of maximum and minimum temperature occur directly as the sun-spots, with small or no intervals.

5. That the times of high and low water of the lakes and river follow behind the sun-spots, inversely, by a double lag—of lake behind rainfall and of rainfall behind sun-spots—the mean of both being four years.

6. That the periods of maximum and minimum sun-spots, temperature, and rainfall have an intimate relation to each other, and that this relation appears in the respective periodicities, which differ but little, while the means are nearly identical.

The question naturally arises, How far do the conclusions here recorded afford a foundation for forecasting the meteorology of the future?

If all the wave periods were of equal lengths and time?, with sufficient allowance made for other factors not within our present discussion, we ought to do so with exactitude. But though our sovereign governor—the sun—exhibits a considerable degree of regularity in the increase and decrease of his spots, he has not as yet admitted us into the secret either of the cause or of the extent and frequency of his variations.

We have also seen that while the curves of temperature and rainfall are controlled by the sun-spot periods, their times of maxima and minima are not therefore synchronous. This is true to some extent as between the sun and the temperature, while those of the rainfall are not only inverse to, but lag behind, the temperature extremes, with varying times. There follows, therefore, a difference, both in the lengths and the times of the periodicities of each. Owing to this lag, and its variation in time of one to four years, it follows that when the temperature curve is at its maximum or its minimum, that of the rainfall is not necessarily at its lowest or its highest. In fact, such a conjunction may be brought about in the progress of time, that a wet period may correspond in time to a warm one, or nearly so, and vice versa, and yet the law of opposites continue absolutely persistent.

This observation applies with even greater force to the lake curves, the lag in which is uniformly greater than in those of precipitation. Thus it has happened three times within the last half-century that high water in Lake Erie has corresponded in time with a high sunspot period.

We observe, also, in noting the curves of temperature, as each approaches its low extreme, a sudden dropping of the temperature from