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 XIII. Intelligence and Miscellaneous Articles, 



ON THE PERIODIC RETURN OF THE MINIMUM OF SUN-SPOTS; 

 THE AGREEMENT BETWEEN THOSE PERIODS AND THE VARIA- 

 TIONS OF MAGNETIC DECLINATION. BY ROD. WOLF. 



SINCE the time when the Academy was pleased to take an interest 

 in my observations establishing a relation between sun-spots and 

 terrestrial magnetism, I have continued the study of these phsenomena, 

 and have examined at least four hundred volumes, in order to make 

 myself acquainted with all the observations of sun-spots. The result 

 is a memoir, which I shall shortly complete, the contents of which 

 appear to me of sufficient importance to warrant my presenting a 

 brief report of them. The memoir is divided into six sections, as 

 follows: — 



In the first chapter it is proved, by means of the six different 

 epochs established by the minimum and maximum of sun-spots, that 

 the mean duration of sun-spots maybe fixed at 1 1*1 11 =0*038 year, 

 so that nine periods are exactly equivalent to a century. 



In the second chapter it is proved, that in each century the years 

 0-00, 11-11, 22-22, 33-33, 44-44, 55-56, 66-67, 77-78, 88-89 cor- 

 respond to the minimum of sun-spots. The interval between the 

 minimum and the succeeding maximum varies. The mean is five 

 years. 



The third chapter contains an enumeration of all the observations 

 of sun-spots from the time of Fabricius and Scheiner to Schwabe, 

 always placed parallel with my periods. The agreement is astonishing. 



The fourth chapter establishes the remarkable analogies between 

 the sun-spots and the variable stars, from which it may be admissible 

 to infer an intimate connexion between these singular phsenomena. 



The fifth chapter demonstrates that my period of 1 T 1 1 1 years 

 coincides still more exactly with the variations of the magnetic de- 

 clination than the period of 1 O^- years assumed by M. Lament. The 

 magnetic variations even follow the sun-spots, not only in their 

 regular changes, but also in all their smaller irregularities ; and I 

 think that this latter remark will suflice to prove this important 

 relation. 



The sixth chapter treats of a comparison between the solar 

 period and the meteorological indications contained in a Zurich re- 

 gister for the years 1000-1800. The result is, in accordance with the 

 idea of Sir W. Herschel, that the years in which the spots are more 

 numerous are also drier and more fertile than others; the latter, on 

 the contrary, being moister and stormy. The aurora borealis and 

 earthquakes mentioned in that register predominate strikingly in the 

 years of sun-spots. — Comptes Rendus, vol. xxx. pp. 19, 705. 



RESULT OF SOME EXPERIMENTS ON THE CHEMICAL ACTION OF 

 LIGHT. BY J. W. SLATER, ESQ. 



These experiments were undertaken chiefly in order to examine 

 the law proposed by Grothuss, that substances are most readily de- 

 colorized by rays of light of a colour complementary to their own. 

 The solutions used for isolating the different rays were, bichromate 

 of potash for yellow, mixed chlorides of copper and iron for green, 



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