Page:Popular Science Monthly Volume 32.djvu/394

380 other important factors—barometric changes, winds, magnetic and other phenomena. The conclusions of this paper are deduced only from the data presented. Let us now compare the curves.

The maximum temperature periods of 1839, '49, '60, '70, and '82 at Detroit will correspond to the minimum rainfall periods of 1839, '50, '60, '72, and '86—if we credit to the latter a lag or interval behind the temperature periods of to 4 years. The minimum temperature periods of 1834, '43, '55, '66, and '75 correspond to the maximum, rainfall years 1836, '44, '55, '68, and '80, with a lag varying from to 5 years; the mean of the lag being 1·8 years.

If this showing reverses the commonly received opinion that high temperature is followed by extreme rainfall, I can only say that the facts, as I find them, do not warrant such conclusion. Let the reader attempt to connect either the maxima or the minima of the curve of temperature with the like periods of the rainfall, and he will find it necessary to admit intervals of from six to nine years, a conclusion which would be inconsistent with any influence whatever.

I now turn to another element, or phenomenon, which will be found to have an intimate bearing upon our investigation.

Recently, much speculation has been elicited by the ascertained periodicity of spots on the sun's disk. It is now an admitted fact that the increase and decrease of the spots affect the magnetic needle, and influence the earth's magnetic and electrical condition. The extent to which these affect the meteorology of our planet is a moot question with the learned on these subjects.

Some noted observers in Europe and India maintain the theory of an influence exerted by the sun-spots upon the rainfall, and this directly as the number of the spots. In this lake region, attempts to establish or define these relations have been few and unsatisfactory. It will be my part to show that the sun-spots do decidedly influence the temperature, and indirectly the rainfall, and that the curves of temperature correspond directly with those of the sun spots. This 'correspondence holds not only as regards the maxima and minima periods, but as to the general features of the two curves.

Wolf's tables of the sun-spots from 1769 to 1882 show ten periods of maxima and as many of minima, the spots ranging from in a minimum year to 150 in a maximum year. Of these periods, one half are embraced within the sixty-six years from 1769 to 1834. For this cycle there are no reliable statistics of temperature and rainfall; so that my data are confined to the sun-spots and the lake periods, of which I present a tabular statement, as supplementary to Diagram No. 1.

Table No. 1 exhibits in groups:

1. The years of maximum and minimum sun-spots from 1769 to 1834, according to Wolf's numbers—the maxima and minima in separate columns.