494 POPULAR SCIENCE MONTHLY 



earthquakes and volcanic eruptions are most frequent and most in- 

 tense during the years shortly before and after sunspot minima. 



In order to estimate the reliability of Jensen's conclusion, it is 

 necessary, first, to eliminate the personal equation by comparing his 

 data with another set compiled independently; and, second, to eliminate 

 accidental or sporadic occurrences and faulty observations by an appeal 

 to averages. It has been possible to accomplish the first result by means 

 of data which Mr. Eobert W. Sayles, of Harvard University, has kindly 

 put at my disposal. In the pursuit of certain researches having no 

 immediate connection with the problem in hand, he had prepared a 

 table showing the years of occurrence of notable earthquakes and 

 eruptions from 1755 to 1902. He had divided the years into three 

 classes according to the severity and number of the phenomena of both 

 sorts in each year. He has kindly prepared the accompanying diagram 

 (Fig. 1), showing, on the one hand, the years of telluric activity by 

 means of the row of dots at the bottom, and, on the other, the number 

 of sunspots by means of the wavy line. The open circles indicate years 

 when notable earthquakes or eruptions occurred, although not in large 

 numbers, nor of exceptional severity. They are reckoned as unity. The 

 solid round dots represent years of greater severity than the preceding, 

 and are reckoned as having a value of two in computation. The solid 

 squares indicate extreme severity, and are reckoned at three. To the 

 diagram as prepared by Sayles, I have added Jensen's data, as appears 

 in the small rectangles above the sunspot curve. Jensen, unlike Sayles, 

 has separated earthquakes and volcanic enrptions. Earthquakes are 

 shown above the heavy horizontal line, and eruptions below. The size 

 of the rectangles indicates Jensen's estimate of severity and frequency 

 combined. For convenience of reference I have added the appropriate 

 numerals. 



The data of Sayles and Jensen supplement each other admirably. 

 Neither investigator lays claim to absolute completeness in his data; 

 but, on the contrary, both express regret that they have not been able to 

 obtain fuller information. Nevertheless neither appears to have' 

 omitted any phenomenon of first-class importance. The method of 

 compilation was quite different in the two cases. • Sayles lays special 

 stress upon the severity of individual earthquakes or eruptions; while 

 Jensen emphasizes the total number of occurrences in a given year. 

 The two sets of data were prepared without reference to each other; 

 and different sources of information were evidently used, as appears 

 from the relatively large importance which Jensen, an Australian, 

 naturally assigns to the phenomena, of Oceania. For instance, to illus- 

 trate the difference in the point of view, Jensen gives to 183^ the value 

 of 6; while Sayles makes it one of the severest years, which on Jensen's 



