LJUNGMAN SECULAK PERIODICITY OF HERRING FISHERIES. 499 



h. By reckless fishing, thus depriviug the herring of his necessary 

 food. 

 C. Under the third head would come all natural causes : 



1. The herrings have been destroyed by the unfavorable condition of 



the weather, by an unusual number of fish of prey and birds of 

 prey, by lack of food, &c, by various natural causes hurtful to 

 the roe, the young fish and the fully-grown fish. 



2. The herrings were obliged to leave the coast in consequence of — 



a. Changes in its physical condition both meteorological and hydro- 

 logical (accidental or periodical), as likewise changes in the nature 

 of the bottom, principally at the spawning places. 



b. Changes of a biological nature, e. #., an increase in the number 

 of fish of prey or birds of prey ; lack of food, or changes in the 

 character of the local fauna and flora, occasioned by overwhelming 

 masses of herrings flocking towards one point. 



c. A secular periodicity in the natural condition of the whole region 

 where herrings occur, thus obliging the large schools of herrings 

 to change their spawning-places and their places of sojourn dur- 

 ing the early part of their life. 



Of all these explanations only the last mentioned shall form the sub- 

 ject of further remarks, and it will be our object to find out whether 

 there is really any secular periodicity in nature sufficiently strong to 

 cause the disappearance of the herrings from certain coasts. 



In the year 1843 the well known astronomer, Mr. S. H. Schwabe, at 

 Dessau, succeeded in proving that the solar spots known since the second 

 decade of the seventeenth century were periodical in their occurrence ; 

 and in 1852 it was found that " the daily variation of the magnetic 

 needle lasted exactly as long as the period of the solar spots, and that this 

 variation reached its utmost limit at the time when the solar spots were 

 most numerous, and was scarcely noticeable when the solar spots were 

 fewest in number." The average length of the solar-spots period was 

 by Wolff found to be 11.11 years ; Schwabe had previously put it at 

 10 years, and Lainont, in Munich, at 10.48; whilst Wolff, Fritz, and 

 others proved conclusively that there were longer solar-spots periods, 

 comprising about fifty-five and one-half years. Other scientists, how- 

 ever, put the length of the longer periods at a different figure, e. g., 

 Koppen at forty-five years, Lemstroin fifty-eight, Klein sixty- seven, and 

 Hornstein seventy. In 1862 Fritz, and in 1873 Koppen showed a cor- 

 respondence in the occurrence of northern lights and the changes in 

 the solar-spots periods.* Thus evidence was constantly accumulating 

 to prove the great influence which the solar spots exercise on our earth. 

 Among the evidence bearing more directly on our question the most 

 important is doubtless the correspondence between the occurrence of 

 the northern lights and the solar spots discovered by Fritz, and the fact 



*Thc periodicity of the northern lights had already been spoken of during th >. last 

 century by Mairan, Wargtnlin, Th. Bergman, and others. 



