362 
REPORT —1854. 
which corresponds in a manner and to a degree which can scarcely be ima¬ 
gined to be accidental, with an analogous fluctuation which recent observa¬ 
tion has also discovered in those affections or obscurations of the sun's disc 
which arc known to us by the name of the solar spots. It is unnecessary 
that I should occupy your time by entering into questions much discussed 
by philosophers, iu regard to the probable physical nature of these spots; it 
will suffice to state the fact, that when the* sun is viewed with a telescope, his 
luminous disc is found to be scarcely ever free from dark or ashy-colourcdspots 
of irregular and variable outline, appearing 'and disappearing »t uncertain 
times, and having no fixed period of duration. They are occasionally, though 
rarely', so large as to be visible to the naked eye when the brightness of the 
sun is partially veiled by thin clouds or by vapours. Fur several years past 
the solar spots have been the subject of cureful daily observation, particularly 
in Germany, by which it has been learned that the number of the spot*, and 
the space they occupy on the solar disc, vary considerably at different time, 
and that the variation is of a character which we can by no means regard as 
accidental, since it follows with great regularity a law nf periodical alternate 
increase and decrease, continuous and progressive from a minimum to a 
maximum in a period which corresponds nearly with five of our years f and 
from a maximum to a minimum in a period of similar duration. Several such 
periods of alternate increase and decrease have now been observed, so as 
thoroughly to establish the fact and the regularity of its occurrence, the 
spots usually appear in groups, and to give a notion of the magnitude and 
the variation of their number at different times, it may be stated that in the 
years of minimum the number of distinct groups appearing iu the year'» 
usually between thirty and forty; whilst in the.years of maximum the num¬ 
ber is between 300 and 4-00. The years of maximum, since the solar spots 
have been subjected to this careful examination, have been 1828,1837 am 
1848; the years of minimum 1833 and 1843. . ... 
Now, before we come to the parallel circumstances of a decennial periodi¬ 
city in the magnetic disturbances, it may be desirable to premiie a Icj 
words of general explanation respecting these phenomena, of which ho 
greater part of our knowledge is so recent. When the Colonial Magnp 11 
Observatories were established in 1840, little more was known of them than 
the fact, that at uncertain nud apparently irregular times the magnetic' me 
tion nud force were liable to be affected by seemingly capricious ebaugef 
sometimes of very considerable amount, and occasionally succeeding fa |'J 
other with great rapiditythat these affections took pluee at one and W 
same tune in different parts of the continent of Europe;—and that the change* 
which they induced in the magnetic direction and force observed wim" 1 
those limits, were generally simultaneous (in absolute dine), an<itf)8gK« 
degree similar. A connexion had also been inferred between the disturb 
nnces and tl.e aurora borealis, from the circumstance that auroras of rent¬ 
able brilliancy had been frequently known to occur at times when 
netic instruments wore unusually disturbed. Now, the observations at w 
Colon, a| Observatories have, in the first place, extended and rendered 
kn ° w, ^ 1 K e of t,ie generality of these phenomena. They ha 
Z n ! I)arb ° f the 6 lobe »»ost distant from each other are affe^ \ 
but tbat when places thus simultaneously af** 1 
Thn mnsf ^' r^ 0 " 1 eaeh ot,,LT ’ tl "“ ^ts at each mav be very dl*dmil£ 
mr ntsT! £ n 1°. COn, P' , . rison with the variation of the meteorological^ 
duration |,n« ^ C , estabbsb ^ ,e existence of any mutual connexion. 1 
rencc extend?. S ° k een ,0UI1C * t0 be as apparently uncertain as their » 
rence, extending sometimes over three or four successive days withou 
