(912.) 
European 
magnbtical 
observa- 
tories, 
(913.) 
Depen- 
dence of 
magnetic 
periods on 
the sun 
and moon. 
996 
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 
MATHEMATICAL AND PHYSICAL SCIENCE. 
(Diss. VI. 
currents may, in part at least, be of a thermo-electric 
character, or t ects may possibly depend upon 
the direct demagnetising influence of temperature, as 
Dr Faraday supposes (830). The secular magnetic 
changes will Mie ever remain the most unac- 
countable. e 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! It appears also to be indi (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. Lamont, 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 Junar 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. Name. Date of Discovery. Discoverers. 
36 =©Atalanta 1855 Oct. 5 Goldschmidt. 
87 ~=—- Fides Oct. 5 Luther. 
38 Leda 1856 Jan, 12 Chacornac, 
39 Letitia Feb. 8 Chacornac. 
40 Harmonia March 31 Goldschmidt. 
41 Daphne May 22 Goldschmidt, 
42 Isis May 28 Pogson. 
ge 
