488 



NATURE 



{April \%, 1878 



thin iron plate in front of this magnet. I'hese experi- 

 ments are worth repeating by those who desire clearer 

 conceptions of the manner of action of that remarkable 

 instrument. 



SUN-SPOTS AND TERRESTRIAL MAGNETISM 



IN a remarkable article on "LaMctcorologie Cosmique," 

 which has appeared in the Amiuaire of the Bureau 

 des Longitudes, for 1878, M. P'aye says with reference to 

 the influence of sunspots on the earth's magnetism, that 

 the observations of Cassini " give i787"25 for the date of 

 the maximum observed then at Paris, whilst the latest 

 observations — those of Mr. Broun, himself at Trevan- 

 drum — assign 187085 for the epoch of the last maxi- 

 mum. The interval is 83 60 years. On dividing this by 

 8, the number of periods in this interval, io"45 years, are 

 found for the duration of the period. That is to say, 

 almost exactly the value already found by Lamont by 

 means of his own observations at Munich. The period 

 of the spots deduced by M. Wolf, ifi years, not being 

 equal to that for the magnetic variations, these two 

 phenomena have no relation to each other." 



I desire to offer a remark on this conclusion, which 

 seems to me too hasty. On examining the two periodic 

 series, that for the diurnal variation of declination and 

 that for the frequency of the solar spots, we see that 

 there is a perfect coincidence in their phases though the 

 length of successive periods is not constant. We may 

 find a mean length of ten, eleven, or more years, accord- 

 ing to the epoch from which the calculation is begun, but 

 we shall always find the same length from both series if 

 ve commence at the same date. 



It seems to me then that the true way to dttermine 

 whether there is an intimate connection between the two 

 phenomena is to compajc their phases, and see whether 

 the maxima and minima of the one coincide with those 

 ot the other. If there is identity in these respects, we 

 must without doubt find the same mean values for the 

 periods. 



M. Faye accepts the date 1787'25 as that of a maxi- 

 mum for the oscillations of the declination. If we look 

 then at the curve. Fig. 2, given by him in the article in 

 question, we see that this corresponds exactly with a 

 maximum of sun-spot frequency. In like manner similar 

 coincidences are seen in the epochs deduced from the 

 ob^ervations of Arago and others up to the present time 

 when compared one by one with the sun-spot observa- 

 tions of Schwabe, Carrington, Secchi, as well as of those 

 made at Kew, The conclusion seems to me very dif- 

 ferent from that ef M. Faye. We are entitled to apply 

 the rule he has given (p. 634) : " If two series of pheno- 

 mena, however different they may appear at first, follow 

 exactly the same period, they ought to be referred to the 

 same cause." 



There is another passage upon which I desire to offer 

 a remaik : " Two kinds of meteors exercise a consider- 

 able influence on the direction of the magnetic needle, 

 these are the auroras boreales and the cyclones." 



For the first there is a general agreement, but for the 

 cyclores what observations have we which prove any 

 such influence.'* If cyclones exercise a considerable 

 influence on the direction of the needle, in what phase of the 

 phenomenon does this occur ? Is it on their formation, on 

 their passage over some particular meridian, or when their 

 centre is over a place ? In the last case each cyclone will 

 be a source of disturbance, which will be manifested as it 

 progresses, ani not simultaneously at all places, which, 

 however, is what really occurs in the case of magnetic 

 disturbances. Electricity is, without doubt, a cause, but 

 only in the case of such considerable discharges as the 

 aurora polaris ; but not the local electricity which may 

 accompany cyclones. When there is a storm, and the 

 thunder rolls, and the electrometer shows enormous 



variations of atmospheric electricity, changing sign con- 

 tinually, the magnetic needle continues its usual and 

 regular progress. Of this we can offer hundreds of 

 examples, JOAS Capello 



Lisbon, February 22 



P.S.— The mean movements of the magnetic needle in 

 the Lisbon Observatory, from eight A.]\r. to two p.m. are 

 given in Nature, vol. xiii. p. 448, for the years 1858 to 

 1875 ; the following are the corresponding mean ranges 

 for the next two years :— 



1876 5"8i' 1877 5'54' 



So that the mean movement was less in 1877 than in 

 1876. 



OUR ASTRONOMICAL COLUMN 



New Companion to Aldebaran. — Mr. S. W. Burn- 

 ham notifies his discovery with the 185-inch Alvan Clark 

 refractor of the Dearborn Observatory, of a minute star 

 much nearer to Aldebaran than that which makes the 

 double star H. VI. 66; he compares it with the ruddy 

 bright star, as resembling, in difficulty and appearance, 

 Mars and his outer satellite. The mean of three days' 

 observations gives the angle lOQ'^'o, and the distance 

 30" "35 for 1 877*90, or if the second result which, as 

 printed, differs nearly ten degrees from the other two, 

 the angle will be iii°"9. The secular proper motion of 

 Aldebaran, according to Miidler, is \<^"'i in the direction 

 157°; some years must elapse before the question of 

 physical or optical duplicity can be decided. Eight days' 

 measures of the close companion of Sirius, by Mr. ■ 

 Burnham, with the same instrument, assign for the 

 angle of position S2°'4, distance 10" "83 at the epoch 

 1877-97. 



The Star Lalande 37813. — Mr. J. E. Gore writci 

 from Ballisodare, Co. Sligo, with reference to this star, 

 which appears in the reduced catalogue as a second mag- 

 nitude, and which, observing in the Punjab in August, 

 1877, he had found a little less than Lacaille 8308 or 

 7 m. This is one of the errors in the catalogue which, 

 as in a case recently noticed in this column, can only be 

 cleared up by referring to the Histoire Celeste. The 

 observation was made on August 20, 1795, and the star 

 No. 37813 was really estimated 7 '8 m. a Aquilae was 

 observed immediately before it, and entered 2 m. ; it is 

 this erroneous magnitude for the bright star of Aquila 

 that has become attached to the star of which Mr. Gore 

 writes. There is a very noticeable proper motion in 

 N.P. D., apparently about + o''"48 annually, as shown by 

 comparison of the observations of Lacaille, Lalande, 

 Jacob, and Argelander, with the position in the Wash- 

 ington Catalogue for 1 860. 



The Minor Planets. — Discoveries in this group still 

 progress. No. 186 was detected by M. Prosper Henry 

 at Paris, on April 6, shining as a star of 11 -5 m., and 

 No. 187 by M. Coggia at Marseilles, on April 10 ; it was 

 estimated 10 m. No. 178 (Palisa, 1877, November 6) 

 has been named Belisana, and No. 184 (Palisa, 1878, 

 February 28) it is proposed to call Deiopeia. With 

 already seven additions to the list, it would not appear 

 that 1878 is likely to fall short of the most prolific of 

 preceding years in these discoveries. 



The Transit of Mercury on May 6. — If we ca]( u- 

 late strictly from Le Verrier's tables of sun and planet, 

 using therefore the value of the sun's diameter which 

 he deduced from the transits of Mercury in his memoir, 

 printed as an addition to the Connaissnncc des Temps for 

 1848, we shall have the following formula for determining 

 the time of the first external contact of limbs in the 

 approaching transit : — 



t — -^. 13m. IS. - [1-8723] r sin /- [i "90791 ^cos /, cos(I/- 56° 49"j) 



in which / is th? Greenwich mean time of contact, r the 



