POET10N OF THE COSMOS. THE SUN. 291 



rological observations continued for several years at single 

 stations, that one side of the sun (ex. gr. the side which 

 was turned towards the earth on the 1st of January, 1846) 

 has a stronger heating power than the opposite side ( 49 ), 

 have, like the. so-called proofs of the decrease of the sun's 

 diameter deduced from the earlier Greenwich Observations 

 of Maskelyne, led to no certain result. The periodicity of 

 the solar spots, reduced to definite numerical ratios by 

 Hofrath Schwabe, of Dessau, appears to rest on a better 

 foundation. Among the astronomers now living who are 

 provided with excellent instruments, no other one has been 

 able to devote to this subject such persevering attention as 

 Schwabe has done. During the long space of twenty-four 

 years he has often examined the sun's disk for upwards of 

 300 days in each year. His observations of the solar spots 

 from 1844 to 1850 not being yet published, I have been 

 indebted to his friendship for the opportunity of consulting 

 them, and at the same time for answers to many questions 

 which I proposed to him. I close the present section, on 

 the physical constitution of the central body of our system, 

 with the results with which his kindness has enriched the 

 astronomical portion of my work : 



" The numbers contained in the following table leave no 

 room to doubt that, at least from the year 1826 to 1850, 

 the solar spots have shown a period of about ten years, with 

 maxima in 1828, 1837, and 1848, and minima in 1833 

 and 1843. I have had no opportunity of becoming ac- 

 quainted with any continuous series of earlier observations, 

 but I readily admit that the period may be a variable 

 one 4 9i : 



