236 ON THE PERIODICITY OF THE AURORA BOREALIS. 



years more exactly than to Lamonfs period of 10.43 years, or Sabine's of only 10 years. 1 

 Wolf claims that the phenomena of the earth's magnetism run parallel with those of the 

 sun's spots not only in their general march but in all their exceptional digressions. 

 Lamont reposes less confidence than Wolf in the earlier observations not only of the 

 sun's spots but also of the magnetic elements ; and in this opinion the astronomer John- 

 son - appears to coincide. Lamont admits merely a general resemblance without any 

 minute coincidence in the progress of the two classes of phenomena. His words are : — 



" Das jedenfalls merkwiirdige Zusamrnentreffen der Maxima und Minima bei den magnetischen Bewegungen und den 

 Sonuenllecken kann hiernack als ein eigentUcher Causal-Xexus nickt crkauut wtrden, &e." 8 



Wolf insists that his formula, 



B= 6.273 +0.051 a, 



in which B is the variation in magnetic declination and a the relative number of spots, 

 represents the magnetic observations at Munich, from 1S35 to 1850 inclusive, as ac- 

 curately as Lamont's formula for the declination derived from the observations them- 

 selves, — 



B = 8'.70 -4- 2'.1 sin. [72°.58 + n. 34°.84], 



(n) being the years elapsed since the epoch, 1848. Wolf afterwards modified this 

 formula, and obtained similar ones for other localities. 4 



W. Herschel and Gruithuisen inferred from then- own comparisons that an abun- 

 dance of solar spots was accompanied with an increase in the mean temperature of the 

 earth. Arago arrived at the opposite conclusion from observations made at Paris be- 

 tween the years 1826 and 1851. Secchi's observations in Rome corresponded with 

 Ai-ago's conclusion. Wolf has renewed the incpoiry, and with enlarged materials has 

 sought to reconcile the apparent incongruity here exposed by the fact that between 

 the years 1760 and 1802 the mean temperature was highest in years rich in solar 

 spots, whereas the opposite rule held between the years 1803 and 1847. On this sub- 

 ject a paper by Gautier 5 of Geneva may be consulted to advantage. It will be a 

 wonderful fact, whenever it is established, that changes in the number and activity of 



> Bulletin de l'Acad. Royale de Brux. 2 S. VI. 358, 9. 2 Memoirs of the Astronomical Society of London, XXVI. 201 . 



8 Sitzungsberichte der Koniglich. Bayer. Akad. der Wissensch. 1862, II. Heft II. 74. 



4 Vierteljahrsschrift der Natnrforsch. Gesellsch. in Zurich, IV. 222, 223, VI. 416, IX. 120, and X. 361. 



6 Annales de Chimie et de Physique, XII. 57-67 ; Bibliotheque Universelle, LI. 327. 



