496 POPULAR SCIENCE MONTHLY 



two rectangles marked 2 and 6 above it. Therefore in calculating the 

 data for the three curves of Figs. 2 and 3 it counts one in every case. 

 So too does 1868, although it was a } T ear of greater severity as is indi- 

 cated by the solid square below the curve and the rectangles marked 

 12 and 8 above it. The year 1869, however, having only a single 

 rectangle with a value of two, counts only in the computation of the 

 data for the solid line of Fig. 3. 1870, on the other hand, is reckoned 

 as one in computing the curve of Fig. 2 and the dotted line of Fig. 3. 

 With 1870, which was a maximum year, we cease to count the years 

 as being after the preceding minimum. 1871 is reckoned not as four 

 years after 1867, but as seven years before the minimum of 1878, 

 and so forth. By adding the figures for all the sunspot waves, and 

 plotting the results, we get the simple frequency curves of Figs. 2 and 3. 

 Figs, -i and 5 are derived in the same way, except for one thing. Instead 

 of reckoning each year of the occurrence of earthquakes or eruptions as 

 having a value of only one, each is reckoned according to the value 

 given it by Sayles or Jensen, respectively, as shown by the character or 

 size of the spots and rectangles of Fig. 1. An inspection of the four 

 curves of Figs. 2 to 5 shows that they agree in essential points. Each 

 of the six curves, two for Sayles, and four for Jensen, has a pro- 

 nounced maximum at or within a year of the time of sun-spot mini- 

 mum. That is, when sunspots are fewest, earthquakes and volcanic 

 eruptions are most numerous and most severe. 



The four curves of Figs. 6 to 9 on the right-hand side of page — 

 were drawn in exactly the same way as the four which lie beside 

 them (Figs. 2-5), except that the sun-spot maxima were used as the 

 reference points instead of the minima. They are introduced by way 

 of contrast. It is evident that telluric activity is weak at times of 

 sun-spot maxima. All the curves of Figs. 2 to 9 show the lack of 

 symmetry characteristic of sun-spot variations. The lapse of time from 

 maximum to minimum is greater than from minimum to maximum. 



Having seen that there is a coincidence of some sort between sun- 

 spot minima and seismo-volcanic maxima, the next step is to compare 

 the mean sun-spot curve from maximum to maximum with the mean 

 seismo-volcanic curve for the same period. The mean sun-spot curve 

 is, of course, easy to obtain. Figs. 10 to 13 show the first stages in 

 the construction of the mean seismo-volcanic curve. The time from 

 one sun-spot maximum to the next is divided into eight periods as 

 follows : 



1. The year of maximum spots. 



2. The year succeeding that of maximum spots. 



3. An intermediate period of decreasing number of spots, — average 

 length about 3% years. 



