1904.] Sunspot Variation in Latitude, 1861 — 1902. 



From a valuable series of sunspot observations, made between the 

 years 1853 and 1861, Kichard Carrington* was the first to point out 

 that spots had a general drift towards the Equator during a sunspot 

 cycle, or, to use his own words, there was indicated " a great con- 

 traction of the limiting parallels between which spots were formed for 

 two years previously to the minimum of 1856, and, soon after this 

 epoch, the apparent commencement of two fresh belts of spots in high 

 latitudes, north and south, which have in subsequent years shown 

 a tendency to coalesce, and ultimately to contract, as before, to 

 extinction." Sporer fortunately took up the work where Carrington 

 left off, and his observations extended over the period 1861 — 1879. 

 These were published in four different volumes,! and the conclusions 

 at which he arrived practically corroborated those of Carrington. 

 In the last of these publications, Sporer summed up all the observa- 

 tions for the period 1854—1879, and published curves, showing the 

 relation between the sunspot frequency for these years and the 

 variation of the mean heliographic latitude of the spots. 



The law of zones, as definitely formulated by Sporer, is as 

 follows; : — " Un peu avant le minimum, il n'y a de taches que pres 

 de l'equateur solaire, entre +5° et -5°. A partir du minimum, les 

 taches, qui avaient depuis longtemps deserte les hautes latitudes, s'y 

 montrent brusquement vers ± 30°. Puis elles se multiplient, un pen 

 partout, a peu pres entre ces limites, jusqu'au maximum, mais leur 

 latitude moyenne diminue constamment jusqu'a l'epoque du nouveau 

 minimum." 



As solar prominences appear on any part of the disc, it was 

 sufficient, in order to trttce their distribution, to divide the suns 

 surface into nine zones of 10 degrees each. Since, however, spots 

 seldom occur above latitude 40°, the width of the zones had to be 

 considerably diminished. For the present inquiry, it was finalij T 

 decided to group the spots into belts 3 degrees wide, for even zones 

 of 5 degrees in width were found to mask many important charac- 

 teristics. 



The necessity for such narrow zones will be seen from the accom- 

 panying figure (fig. 1), in which the yearly distribution of spots 

 is shown for the years 1879 — 1883, taking zones of 10 degrees, 

 5 degrees, and 3 degrees in width respectively. 



* ' Observations of the Spots on the Sur.,' made at Redlrill by K. C. Cariington, 

 F.R.S., 1863, p. 17. 



f 'Publication der Astronomiscben G-esellschaff.,' vol. 13 (Leipzig. 1874); 

 'Publication der Astronomiscben (ieselisclmlt,' vol. 13. Fortsetzung (Leipzig, 

 187fi) ; ' PuWicationen des Astrophysikalischen Observatoriums zu Potsdam,' No. i, 

 vol. 1, Part I ; No. 5, vol. 2, Part I. 



X ' Comptes Pendus,' vol. 108, p. 486. 



