382 THE POPULAR SCIENCE MONTHLY. 



shall sec presently how far these statements tally with the data drawn 

 from fuller sources, for the half-century succeeding. 



Let us now turn to Diagram No. 2, which exhibits the sun-spot 

 curves from 1834 to 1884, paralleled with those of the temperature, 

 the rainfall, and the lake. 



We see five " periods " of sun-spot maxima, culminating in the 

 years 1838, '48, '60, '70, and '82, the number of spots at each varying 

 from 95 to 150. And five of sun-spot minima — in the years 1834, 

 '44, '5G, '67, and '77, the spots in each varying from 5 to 10. The 

 maximum periods recur at intervals of ten to twelve years — and the 

 minimum periods at like intervals — the means being 10'8 years. With 

 the aid of the accompanying Table No. 2, we may proceed to compare 

 results. 



Table No. 2 aims to give in a succinct form all the data which our 

 discussion requires. These are grouped in columns, as follows : 



The first group gives (in three columns) the sun-spot data, in 

 the same manner as in Table No. 1, viz., the years of maxima 

 and minima, the number of spots at each, and the lengths of the 

 periods. 



The second or temperature group gives (in two columns) for those 

 years of maxima and minima which conform to the sun-spot maxima 

 and minima, the degrees of temperature (the mean of the year at De- 

 troit), and the lengths of the periods. 



The rainfall has three groups. The first gives for Detroit (in 

 three columns) the maximum and minimum periods, the precipitation 

 in inches at each, and the lag or interval at which each follows, in- 

 versely, behind those of the temperature. Like data are given for the 

 rainfall at Milwaukee and at Cleveland, so far as I possess data, omit- 

 ting the column of lag. 



For the water-levels there are two groups, each shov»'ing (in three 

 separate columns) the periodicities, the measurements in feet and 

 tenths below the plane of 1838, and the lag behind the rainfall at 

 Detroit. 



Lastly are given (as in Table No. 1) the lag of the lake behind 

 the sun-spot periods — lake maxima behind sun-spot minima, and the 

 reverse. 



My aim is to exhibit those fluctuations in the elements under dis- 

 cussion which conform to the sun-spot periodicities, according to the 

 law which seems to govern, viz., temperature directly as the sun-spots ; 

 rainfall inversely as the temperature ; lake-levels directly as the rain- 

 fall, and the periodical changes in each, following uniformly those of 

 the preceding or influencing element by a lag of short interval ; and 

 this increasing in length according to the remoteness from the original 

 source of influence. 



When we consider that the sun is itself the ultimate source of all 



