MATHEMATICAL AND PHYSICAL SCIENCE. 



[Diss. VI. 



from the minimum, is 6 '4. These observations also 

 fully confirm the progressive motion of the whole 

 system of magnetic lines on the surface of the 

 globe. 



In Europe national, and even private, observa- 

 tories have contributed largely to our knowledge of 

 the laws of magnetism. Among these observatories 

 may be mentioned Greenwich, Dublin, Makerstoun 

 in Scotland, Munich, Prague, Brussels, St Peters- 

 burg, and the numerous other Russian stations. At 

 Greenwich and at Kew, near London, the automatic 

 registration of magnetical and meteorological instru- 

 ments, by means of photography, was introduced by 

 Mr Brooke and Mr Ronalds. It would be impossi- 

 ble in this place to give even a summary of the re- 

 sults obtained from these and the Colonial estab- 

 lishments. Besides the valuable deductions by 

 General Sabine already referred to (910), the careful 

 analysis of the formal laws of magnetism obtained at 

 their respective observatories byM.Lamont.M.Kreil, 

 and Mr Broun (Sir Thomas M. Brisbane's observer), 

 merit special notice. 



The primary cause of the earth's magnetism re- 

 mains involved in the greatest doubt. That it is due 

 to electric currents, and not to permanent magnet- 

 ism, is at least probable ; and it is likely that these 



currents may, in part at least, be of a thermo-electric 

 character, or the effects may possibly depend upon 

 the direct demagnetising influence of temperature, as 

 Dr Faraday supposes (830). The secular magnetic 

 changes will probably ever remain the most unac- 

 countable. The greater portion of those which are 

 obviously periodic seem to depend upon the position 

 and efficiency of the sun in its apparent diurnal and 

 annual course, having their crises at certain hours of 

 the day, and certain seasons of the year. It is un- 

 derstood that the most recent researches leave little 

 doubt as to a like influence arising from the moon's 

 position. 1 It appears also to be indicated (although 

 the induction is perhaps yet incomplete) that the 

 diurnal changes, and also those of a capricious and 

 irregular character (magnetic storms), have a period 

 of greatest and least intensity of fluctuation extending 

 to about ten years, a minimum having occurred in 

 1843, and a maximum in 1848. This nearly coin- 

 cides with a period of greatest and least abundance 

 of the solar spots detected by M. Schwabe, and it is 

 possible that there is a real connection between the 

 phenomena. The first recognition of a ten-year mag- 

 netic period appears to be due to M. Lament, that of 

 a probable concurrence with the frequency of solar 

 spots to General Sabine. 



1 While correcting the press of this page, I have received an interesting paper by General Sabine (Phil. Trans., 1856), in 

 which the dependence of the various magnetic elements on the moon's diurnal place is deduced from a very large number of 

 observations. The change of declination in the course of the lunar day amounts to above 38''. 



Addition to Art. 283, page 860. 

 The following is a continuation of the list previously given of the small Planets : 



No. 

 36 

 37 

 38 

 39 

 40 



Name. 

 Atalanta 

 Fides 

 Leda 

 Laetitia 

 Harmonia 



41 Daphne 



42 Isis 



Date of Discovery. 



1855 Oct. 5 

 Oct. 5 



1856 Jan. 12 

 Feb. 8 

 March 31 

 May 22 

 May 28 



Discoverers. 

 Goldschmidt. 

 Luther. 

 Chacornac. 

 Chacornac. 

 Goldschmidt. 

 Goldschmidt. 

 Pogson. 



