June 27, 1878] 



NATURE 



243 



. T - c , ^ Prague, dec. -range, min., Feb. 28, 



Solar min., June 15, 1843 j ^^ 



^ o \ Pra^e, dec. -range, max., March 



Solar max., Dec. 15, 1847 j 3^, 1848. 



[ Prague, dec. -range, min., March 



Solar_min., Sept. 15, 1855 j-j.j.gy'^jj^j^j;j^ dec-range, min., 

 ( Feb. 15, 1856. 



iKew, dec. -range, max., April 15, 

 Trevandrum, dec. -range, max.. 

 May 15, i860. 



-. , ^, o,, \ Kew, dec. -range, min., August 15, 

 Solar mm., March 15, 1867 I ^gg ^' 



In the next place variations are found in the declination range 

 at Prague which appear to depend on planetary configurations, 

 and which are similar in character to those found at Kew and 

 Trevandrum. 



An inspection of the sun-spot records reveals the fact that 

 at times of maximum spot frequency, not ordy are there most 

 spots on the sun, but that the sun-spot inequalities or oscil- 

 lations (however produced) are at such times much more pro- 

 minent 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 configfurations, we might expect that 

 (possibly from an increase in the susceptibility of the sun) the 

 planetary periods should at times of maximum sun-spots be 

 found to be greater than their average value. 



This is found as a matter of fact to be the case, as will be seen 

 from the following table, comparing together observed sun-spot 

 planetary inequalities for periods of maximum sun-spots with the 

 corresponding mean inequalities : 



If we now turn to declination-ranges we shall find that there 

 are greater oscillations or sub-periods in the value of these 

 ranges during times of maximum than during times of minimum 

 sun-spots. But on the other hand the increased value of such 

 oscillations is by no means so striking as in the case of sun-spots. 

 Mr. Broun has already made the remark that while there is an 

 increase in the whole declination-range during times of maximimi 

 sun-spots, yet this increase is not so marked as in the case of the 

 spots themselve?, inasmuch as we have a considerable declina- 

 tion-range when there are no spots on the sun. From what has 

 now been said it would seem that a similar remark applies to the 

 oscillations or sub-periods of declination-range, which, while 

 increasing from times of minimum to times of maximum sun- 

 spots, do not yet increase so strikingly as the oscillations or sub- 

 periods of the spots themselves. 



If we now treat the inequalities of magnetic declination that 

 appear to depend on the two most available planetary configura- 

 tions in the manner in which we have just treated sun-spot 

 inequalities, we might expect the observed magnetic inequalities 

 corresponding to times of maximum sun-spots to be greater than 



the mean inequalities, but not to the same extent as in the case 

 of sun-spots. 



That this is the case will be seen from the following table, in 

 which observed declination-range, planetary inequalities for 

 periods of maximum sun-spots are compared with the corre- 

 sponding mean inequalities : — 



Period of Mercury. 



, Observed. Mean. 



Between and 30 +11-48 -t- 10-42 



33 ,, 60 -f 3-62 -f 7-25 



60 „ 90 - 3*50 - 2-25 



90 M 120 - 6-91 - 3-25 



,, 120 ,, 150 - 9-13 - 8-16 



150 „ 180 - 12-37 - 11-67 



,, 180 ,, 210 - 13-72 - 12-12 



,, 210 ,, 240 - 10-44 - 8-68 



240 ,, 270 - 2-45 - 2-62 



270 „ 300 -t- 7-73 -+- 4*10 



300 „ 330 + 15-14 + 9*26 



330 „ 360 + I6-20 -f 11-27 



Mercury and Jupiter together. 

 „ Observed. Mean. 



Between o and 30 -1-11-87 -f 11 -61 

 30 „ 60 -f 2-56 -f 8-07 

 60 „ 90 - 4-26 -t- 2-75 

 90 „ 120 - 8-72 - 2-45 

 120 „ 150 - 13-85 - 7-93 

 M 150 ,, 180 - 16-24 - 11-97 

 M 180 ,, 210 - 13-44 - 11-80 

 „ 210 ,, 240 - 8-32 - 8-71 

 ,, 240 ,, 270 + 0-51 - 3-11 

 270 ,, 300 + 11-39 -t- 3-44 

 300 „ 330 -J- 16-91 -1- 8-74 

 „ 330 „ 360 -1- 17*06 -1-11-89 

 It thus appears that in the case of the magnetic decKnation 

 periods there is (as in those of sun-spots) an exaltation of the 

 observed over the mean values during times of maximum sun- 

 spot frequency, but this exaltation is not so marked as in the 

 case of sun-spots. Now, without pretending to know in what 

 way the sun influences the magnetism of the earth, we may 

 imagine that the increased values not only of the average declina- 

 tion-range but also of the sub-periods of these during times of 

 maximum sun-spots may be due to one of two causes, or to both 

 of these together. Thus we may imagine that the sun has an 

 increased magnetic influence during such periods, or we may 

 imagine that there is an increase in the magnetic susceptibility 

 of the earth ; or, finally, we may imagine that both of these 

 causes operate together. The author cannot help thinking that 

 we have some evidence of an increase of the magnetic suscepti- 

 bility of the earth on such occasions derived from two facts dis- 

 covered by Mr. Broun. The one is that the magnetic influence 

 of the moon on the earth shows traces of following the solar 

 period, this influence being greater during times of maximum 

 than during times of minimum sun-spots. The other is that at 

 Trevandrum the lunar magnetic influence, without changing its 

 type, exhibits an increase of value when the sun is above the 

 horizon at that place, as if on such occasions there were an 

 increase of susceptibility to the lunar influence. These, how- 

 ever, are points which can only be determined by a further 

 discussion of observations. 



Geological Society, May 22. — Henry Clifton Sorby, F.R.S., 

 president, in the chair. — ^John Collins was elected a Fellow of 

 the Societ}-. — The following communications were read : — On 

 the serpentine and associated igneous rocks of the Ayrshire 

 coast, by Prof. T. G. Bonney, M.A. — In a paper published in 

 the Quarterly Journal of the Geological Society, vol. xxii. p. 513, 

 Mr. J. Geikie states that the rocks of this district are of sedi- 

 mentary origin, a felspar-porphyry being the '^maximum stage 

 of metamorphosis exhibited by the felspathic rocks," and the 

 diorite, hypersthenite, and serpentine being all the result of 

 metamorphism of bedded rocks. This view is also asserted in 

 the catalogue of the rocks collected by the Geological Survey of 

 Scotland. The author had seen specimens of rocks_ from this 

 district which so closely resembled some from the Lizard, that 

 he visited the Ayrshire coast in the summer of 1877. The 

 author is of opinion that the principal conclusions of the paper 

 referred to above are not warranted by either stratigraphical 

 or lithological evidence. He considers it probable that the 

 " felspar-porphyry," like so much of that in Scotland, is of 

 old red sandstone age, and that the serpentine is of later date. 



