1863.] 235 [Reichenbiic 



" Silliman's American Journal," volume 25, 1858, page 295 (prior 

 to Mr. Wolf's opinion), contains a note, dated 13th January, 1858, 

 in whicli I say, that the period of spots depends on the revolution of 

 Jupiter, and varies principally by the influence of Saturn, as the 

 effects of the other eight planets (I assert the existence of so many) 

 being inferior to that of Saturn, must all fall inside the oscillation 

 produced by the latter. I have farther shown that the maximum of 

 spots corresponds to the aphelion of Jupiter. 



The revolution of Jupiter is 11.86 years. I do not see how the 

 period of spots is shown to be 11.1 years. The time since 1828, the 

 first maximum proved by constant observation, is too short for de- 

 ducing the exact period, which must be variable. Only a long 

 observation can show it to be identical with that of Jupiter, 11.86. 



Remark. As the exact period has not been ascertained, we can in- 

 dulge in the hypothesis, which I, however, feel disposed to reject, that 

 there occur seven maxima within six revolutions of Jupiter, if Saturn 

 steadily advances, and not in the long equally delays the period. For 

 if J/ the mass of Jupiter, m of Saturn, D and d their respective dis- 

 tances from the sun, ^^=; 6, or the tide-creating force of Saturn being 

 i of that of Jupiter, in the sun there will be 7 maxima instead of 6, 

 if there is only acceleration. The period of spots would be 10.17 

 years, and the maxima could oscillate two years before and after the 

 aphelion passage of Jupiter, as in the case of an average period of 

 11.86 they can oscillate 2.4 years. 



We can draw some inferences from the time before 1828. 



In 1779 the attention of William Herschel was turned to the sub- 

 ject of " spots" by a spot visible with the naked eye. We will sup- 

 pose that year one of maximum. The aphelion of Jupiter fell in 

 1780, or the time from 1779 to 1828, the aphelion passage of Jupiter 

 having occurred May, 1827, occupies four revolutions and seventeen 

 months, the maximum having occurred an equal time first before 

 than after the aphelion passage of Jupiter. The period exceeded 

 11.86 years, as afterwards it has been shorter, a circumstance in favor 

 of the average of 11.86 years. The arbitrary period mentioned by 

 Mr. Gregg gives four periods and 4.5 years, a quite unfavorable result. 



Baron Humboldt, in speaking of solar spots, gives a series of ob- 

 servations of different kinds : 



43 a. C. n. Death of Caesar. Dim, cool weather, one year after, 

 political superstition. Falls, however, not two years before the aphe» 

 lion of Jupiter, and coincides with that of Saturn, and can have been 

 a maxiiiuim. 



