April 29, I 



NATURE 



613 



ASTRONOMICAL PHENOMENA FOR THE 



WEEK 1886 MA K 2-8 



/"pOR the reckoning of time the civil day, commencing at 



^■^ Greenwich mean midnight, counting the liours on to 24, 



is here employed.) 



At Greenwich on May 2 

 Sun rises, 4h. 32m. ; souths, iih. S6m. 5o'4s. ; sets, igh. 22m. ; 

 decl. on meridian, 15° 26' N. : Sidereal Time at Sunset, 

 loh. 4m. 

 Moon (New on May 4) rises, 4h. lom. ; souths, loh. 42m.; sets, 

 I7h. 25m. ; decl. on meridian, 5° 29' N. 



Planet Rises Souths Sets Decl. on meridian 



Mercury ... 4 o 



Venus 3 13 



Mars 12 59 



Jupiter 14 49 



Saturn,..- ... 7 26 



10 23 



9 5 

 19 57 

 21 7 



15 38 



Indicates that the setting is that of the folio 



16 46 ... 3 50 N. 



14 57 - 2 18 S. 



2 55* ... 10 39 N. 



3 25* ... 2 43 N. 

 23 50 ... 22 51 N. 



ling. 



OccuUations of Stars by the Moon (visible at Greenwich) 



Corresponding 

 May Star Mag. Disap. Reaj.. tex^'t"ri°"/f"; 



inverted image 

 h. m. h. m. „ „ 



6 ..." Ill Tauri 5i ... 20 12 ... 21 3 ... 114 324 



6 ... 117 Tauri 6 ... 21 42 ... 22 21 ... 88 342 



Saturn, May 2. — Outer major axis of outer ring = 39"'I J 

 outer minor axis of outer ring = 1 7" '4 ; southern surface visible- 

 May h. 

 2 ... I ... Mercury in conjunction with and 0° 6' south 



of the Moon. 

 7 ... I ... Mercury at greatest elongation from the Sun, 

 26° west. 



Positions 0/ the Comet Barnard [ioY Berlin Midnight) 



Log. A 



Bright 



Meteor Showers 

 There are no showers of great importance visible during this 

 week. Meteors from the following radiants have been observed 

 in previous years: — From Crater, R.A. 170°, Decl. 10° S. ; 

 near a Ursie Majoris, R.A. 170°, Decl. 62° N. ; from Virgo, 

 R.A. 202°, Decl. 9° N. ; from Aquila, R.A. 290°, Decl. 10° N. ; 

 and one with radiant at R.A. 234°, Decl. 46° N. 



Stars with Remarkable Spectra 



ON THE FORCES CONCERNED IN PRODUCING 

 THE SOLAR DIURNAL INEQUALITIES OF 

 TERRESTRIAL MAGNETISM » 



T N an article on terrestrial magnetism in the present edition of 

 the "Encyclopaedia Britannica," I have endeavoured to 

 show two things : — 



(i) That of all the various hypotheses which have been started 

 with the view of explaining the solar diurnal inequalities of 

 terrestrial magnetism, the most probable is that which considers 

 these inequalities to be caused by electric currents in the upper 

 regions of the earth's atmosphere. 



(2) That in the neighbourhood of the North Magnetic Pole 

 (judging from observations discussed by Sabine) such currents 

 have in all probability horizontal components flowing in from 

 all sides towards that pole, so that on one side of the pole this 

 component will have a direction the reverse to that which it has 

 on the opposite side of the pole. 



Dr. Schuster (see Report of Magnetical Committee of British 

 Association) has deduced from this the legitimate inference that 

 here we must have a vertical current or component of currents, 

 inasmuch as without this we cannot imagine a series of strictly 

 horizontal currents flowing in from the circumference to the 

 centre like the spokes of a wheel. 



I think it is desirable that this method of discussion should be 

 extended to the phenomena round the magnetic equatoi-. This 

 magnetic equator may be regarded as approximately coincident 

 with the terrestrial equator. It is the line all along which the 

 freely suspended needle points horizontally, just as the magnetic 

 pole is the place 'at which the freely suspended needle points 

 vertically downwards. 



Now a little to the north of the magnetic equator we have, 

 broadly speaking, the following phenomena : — 



(i) When the sun is north of the line, the influence of the sun 

 upon the declination-needle (as represented by that oscillation 

 which culminates an hour or two after noon) tends to drive the 

 North Pole to the west. But when the sun is south of the line 

 this action becomes reversed, and drives the North Pole east- 

 wards. 



(2) Whether the sun is north or south of the line, its action 

 upon the bifilar needle (as represented by that oscillation which 

 culminates about noon) tends to increase the horizontal force. 



Now let us go a little to the south of the magnetic equator, 

 and we find the following behaviour : — 



(3) When the sun is south of the line, the influence upon the 

 declination-needle represented as above tends to drive the North 

 Pole to the east. But when the sun is north of the line this 

 action becomes reversed, and the North Pole is driven west- 

 wards. 



(4) Whether the sun is north or south of the line, its action 

 upon the bifilar needle, represented as above, shows that it tends 

 to increase the horizontal force. 



It is, indeed, well known that there is a norlh-hernisphere and 

 a south-hemisphere action of the sun upon the declination- 

 needle, the one being the reverse of the other, and the southern 

 limit of the first action being the northern limit of the second. 

 And furthermore this boundary line oscillates bacUv/ards and 

 forwards, so that, when the sun is in the north, a station near the 

 equatoi-, but north of it, e.^thibits a more distinctively northern 

 character of oscillation, while, when the sun is in the south, it 

 will exhibit a more or less southern character in its oscillation. 



If we now venture to ascribe the actions represented in (1), 

 (2), (3), and (4) to currents in the upper atmospheric regions, 

 we shall have — 



(i) when the sun is north, caused by a positive current going 

 from south to north ; 



(2) caused by a positive current going from west to east ; 



(3) when the sun is south, caused by a positive current going 

 from north to south ; 



(4) caused by a positive current going from west to east. 

 The resultant of (I ) and (2) would be a horizontal positive 



current going in a direction not far from south-west, and the 

 resultant of (3) and (4) a similar current going in a direction not 

 far from north-west. The analogy in direction as well as oscil- 

 lation to the two systems of anti-tr.ades is at once apparent, and 

 it will be strengthened if we reflect that, in the magnetical as 

 well as the meteorological system, we must have a vertical 

 current at the equator. This current might probably be repre- 



' Being the substance of a Paper recently read before the Literary and 

 Philosophical Society of Manchester, by Prof. Balfour Stewart, F.R.S. 



