314 



DISCUSSION OF THE SECULAR VARIATION 



These differences from the normal values have been thrown into curves, and are 

 given, together with the exhibit of the relative frequency and araoimt of solar spots, 

 in the bottom line of the accompanying plate ; the Atlantic type-curve is shown 

 heavy, the Mississippi type-curve dotted, and the sun-spot curve by a zigzag line, 

 according to Prof E. Wolf's numbers.^ 



The distinguishing features, as described above, of these two type-curves appear 

 well marked, the longer waves of the Atlantic stations show: 

 Principal maxima in 1802 1826 1846 1865 



and principal minima in 1785 1816 1836 1857 



the average interval being about 22 years ; the shorter waves of the interior states 

 show : — 



Principal maxima in 1827 1833 1839 1845 1854 1860 



and principal minima in 1831 1836 1843 1848 1856 1867 



the average interval being about 7 years. These undulations, however, are not 

 sufficiently regular nor sufficiently distinct, being mixed with subordinate fluctua- 

 tions, to serve as a basis of prediction; all that can be claimed for them is a general 

 exponent of the character of the secular change. 



Comparison of the secular variation of the temperature with the variations in the 

 frequency of the solar spots. — It is evident, from the preceding statements respecting 

 the average duration of successions of warmer and colder years, that no intimate 

 relation appears to exist between the two phenomena — they seem to have no feature 

 in common, the sun-spot period of about 11 years is not systematically followed by 

 any of the temperature waves; the chief characteristic of connection, that of equality 

 of average periods, being wanting, we necessarily have coincidence, viz., greater 

 development of sun-spots corresponding to greater cold, as for the years between 

 1810 and 1822, as well as opposition, viz., a greater development of sun-spots 

 during a time of increased heat, as for the years 1799 to 1806, and in general we 

 have phases of the two curves presented in all possible combinations. If we con- 

 sider the small difference in the radiating energy of the surface of a spot and of the 

 unbroken surface of the sun, as well as the comparatively small collective area of 



' Prof. Wolf's relative numbers of sun-spots; from Astronomische Nachrichten, Nos. 1978 

 (March, 1SY4) aud No. 2014 (Nov. 1814), those prior to 1759 from his " Mittheiluiigen." 









I 



2 



3 



4 



5 



6 



7 



8 



9 



1740 





















63,8 



1750 



68.2 



40.9 



33-2 



23.1 



I3-S 



6.0 



8.8 



30-4 



38.3 



48 



6 



1760 



48 



9 



75.0 



SO 



6 



37 



4 



34 



5 



23 







17 



5 



33-6 



52 



2 



108 



3 



1770 



79 



4 



73-2 



49 



2 



39 



8 



47 



fa 



27 



5 



55 



2 



63.0 



94 



8 



90 



2 



I7S0 



72 



6 



67.7 



33 





22 



5 



5 







21 





6S 



6 



104.8 



107 



8 



no 



7 



1790 



84 



4 



53-4 



47 



5 



40 





34 



^ 



22 



5 



15 



I 



7,8 



4 



4 



10 



2 



1800 



18 



.5 



38.6 



=i7 



8 



6S 







75 







50 







25 







15.0 



7 



2 



3 



4 



I8I0 











1.2 



5 



4 



13 



7 



20 







35 







45 



5 



43-5 



34 



I 



22 



5 



1820 



8 



9 



4-3 



2 



9 



I 



S 



6 



7 



17 



4 



29 



4 



39-9 



52 



5 



53 



5 



1830 



59 



I 



38.8 



22 



5 



7 



S 



II 



4 



45 



5 



96 



7 



III.O 



82 



6 



68 



3 



1840 



.S« 



8 



29.7 



19 



5 



8 



6 



13 







57 







47 







79-4 



100 



4 



95 



6 



1850 



64 



■i 



61.9 



S2 





37 



7 



19 



2 



6 



9 



4 



2 



21.6 



50 



9 



Qb 



4 



i860 



98 



6 



77-4 



59 



I 



44 







46 



9 



30 



5 



16 



3 



7-3 



37 



3 



73 



9 



IS70 



139- 1 



111,2 



101.7 



66.3 













1 



