THE SUN'S SPOTS. 397 



individual spots, that one side of the Sun (for instance the 

 side which was turned towards the Earth on the 1st of January, 

 1846) possesses a more intense heating power than the oppo- 

 site one," have not led to more reliable results than the older 

 Greenwich observations of Maskeleyne, which were supposed 

 to prove that the Sun had decreased in diameter. 



The observations made by Councillor Schwabe, of Dessau, 

 for reducing the periodicity of the Sun's spots to definite 

 numerical relations, appear to have a surer foundation. No 

 astronomer of the present day, however admirable may have 

 been his instruments, could have devoted his attention more 

 continuously to this subject than Schwabe, who, during the 

 long period of twenty-four years, frequently examined the Sun's 

 disc upwards of 300 days in the year. As his observations 

 of the Sun's spots from 1844 to 1850 have not yet been 

 published, I have presumed so far on our friendship as to 

 request that he would communicate them to me, and at the 

 same time answer a number of questions which I proposed 

 to him. I will close this section of the Physical Constitution 

 of our Central Body, with the observations with which this 

 observer has allowed me to enrich the astronomical portion 

 of my work. 



' The numbers contained in the following table leave no 

 doubt that, at least from the year 1826 to 1850, the occur- 

 rence of spots has been so far characterized by periods of 

 ten years, that its maxima have fallen in the years 1828, 1837, 

 and 1848, and its minima in the years 1833 and 1843. I 

 have had no opportunity," says Schwabe, " of acquainting 

 myself with the older observations in a continued series, but 



n Compare Nervander of Helsingfors, in the Bulletin de 

 la Classe Physico-Mathem. de I'Acad. de St. Petersburg, 

 torn. iii. 1845, pp. 30-o2: and Buys-Ballot, of Utrecht, in 

 Poggeud. Annaltn dtr l^uysik, vol. Ixviii. 1646, pp. 205-213. 



