1878.] 



Magnetic Decimation at Prague. 



397 









Venus and 



Period of 



Mercury and 



o 





o 



Mercury. 



Mercury. 



Jupiter. 



Between 120 



and 



150 



-25 76 



-816 



-3-48 



150 



n 



180 



-17 -82 



• -6 -94 



-3-36 



180 



11 



210 



- 5-34 



-3 -50 



-2-85 



210 



11 



240 



+ 6-08 



+ 2-91 



-1 -29 



240 



11 



270 



+ 4-79 



+ 7-31 



-0-17 



270 



11 



300 



+ 2-53 



+ 9 70 



+ 1-05 



300 



11 



330 



+ 14 -64 



+ 8-66 



+ 1 '12 



330 



11 



360 



+ 25 -37 



+ 3-96 



-0-31 



These three planetary periods, as shown by the mean magnetic results 

 of the three Observatories recorded in Table IX, are exhibited in 

 Diagram II, in which fig. 2 denotes the period of Mercury, fig. 4 that 

 of Mercury and Jupiter, and fig. 6 that of Mercury and Yenus, while, 

 as shown by the sun-spot results of Table X, they are exhibited in 

 figs. 1, 3, and 5, fig. 1 denoting the period of Mercury, fig. 3 that of 

 Mercury and Jupiter, and fig. 5 that of Mercury and Venus. 



11. If we compare together the three sun-spot periods with the 

 three magnetic periods, as exhibited in these diagrams, we shall remark 

 a great similarity between them, while, however, as we might expect, 

 the declination results lag behind the solar results in point of time. 



12. An inspection of the sun-spot records reveals the fact that at 

 times of maximum spot frequency, not only are there most spots on 

 the sun, but that the sun-spot inequalities or oscillations (however 

 produced) are at such times much more prominent than during times 

 of minimum sun-spot frequency. Now, if it be true that these spot 

 periods are due in a great measure, if not entirely, to planetary con- 

 figurations, we might expect that (possibly from an increase in the 

 susceptibility of the sun) the planetary periods herein investigated 

 should at times of maximum sun-spots be found to be greater than 

 their average value. 



13. I have endeavoured to test this in the following manner : — 

 The two most available periods are that of the orbit of Mercury 



round the sun, and that of the synodic revolution of Mercury and 

 Jupiter. The average sun-spot inequalities for a single period of 

 each of these have already been given in Table X. Now, it might be 

 supposed that we have only for the present purpose to take these 

 periods and find whether their values, during times of maximum sun- 

 spots, are greater than their mean values. It is, however, a curious and 

 interesting fact that (as far back as accurate observations extend) times 

 of many sun-spots correspond well with times when Jupiter is at the 

 perihelion of Mercury. Now, it is easy to see that on this account 

 alone, and apart from any increased susceptibility of the sun, we should 

 have sun-spot inequalities greater than the average at the times when 

 the two planets are in this position with respect to each other. For 



2 d 2 



