Royal Society, 469 



what it does when exposed to those which tend to magnetize it 

 in the opposite direction. An electrolytic magnet, however, 

 always retains a preference for magnetism similar to that origi- 

 nally impressed upon it, though this preference is not always 

 equally strong. On the hypothesis of rotatory particles, this is 

 precisely what might have been expected. 

 Erlangen, July 1860. 



LXIV. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from p. 400.] 



March 8, 1860. — Sir Benjamin C. Brodie, Bart., Pres., in the Chair. 



THE following communication was read : — 

 "On the Solar-diurnal Variation of the Magnetic Declination 

 at Pekin." By Major-General Edward Sabine, R.A., Treas. and 

 V.P.R.S. 



When the first year of hourly observations of the declination, 

 January 1 to December 31st, 1841, was received at Woolwich from 

 the Magnetic Observatory at Hobarton, and when means had been 

 taken of the readings of the collimator-scale at the several hours in 

 each month, and these monthly means had been collected into an- 

 nual means, it was found that the mean daily motion of the declina- 

 tion magnet at Hobarton presented, as one of its most conspicuous 

 and well-marked features, a double progression in the twenty-four 

 hours, moving twice from west to east, and twice from east to west ; 

 the phases of this diurnal variation were, that the north end of the 

 magnet moved progressively from west to east in the hours of the 

 forenoon, and from east to west in the hours of the afternoon ; and 

 again from west to east during the early hours of the night, return- 

 ing from east to west during the later hours of the night : the two 

 easterly extremes were attained at nearly homonymous hours of the 

 day and night, as were also the two westerly extremes ; the ampli- 

 tudes of the arcs traversed during the hours of the day were con- 

 siderably greater than those traversed during the hours of the night. 



When, in like manner, the first year of hourly observations, July 

 1st, 1842, to June 30th, 1843, was received from the Toronto Ob- 

 servatory, and the mean diurnal march of the declination magnet 

 was examined, it was found to exhibit phenomena in striking corre- 

 spondence with those at Hobarton. At Toronto also a double pro- 

 gression presented itself, of which the easterly extremes were attained 

 at nearly homonymous hours, as were also the westerly ; whilst the 

 hours of extreme elongation were nearly the same (solar) hours at 

 the two stations, but with this distinction, that the hours at which 

 the north end of the magnet reached its extreme easterly elongation 

 at Hobarton were the same, or nearly the same, as those at which it 

 reached its extreme westerly elongation at Toronto, and vice versa. 

 Pursuing, therefore, the ordinary mode of designating the direction 

 of the declination by the north end of the magnet in the southern 

 as well as in the northern hemisphere, the diurnal motion of the 

 magnet may be said to be in opposite directions at Hobarton and 



