200 
MAGAZINE OF SCIENCE AND ART. 
restial magnetic forco which re-awakened the atten¬ 
tion of the scientific world to the subject. It was in 
the Committee-Booms of this Association thas the first 
step was taken towards that great magnetic organiza¬ 
tion which has home so much fruit: it was here that 
the philosophical sagacity of Herschol guided its earlier 
career; and it was here again that that the cultivators 
of the science assembled, from every part of Europe, to 
deliberate about its future progress, it was natural, thore- 
fore, that the results obtainedfrom such beginnings should 
form a prominent topic in the addresses which have 
been annually delivered from this chair; and the same 
circnmstances will plead my excuse if I now revert to 
some some of them which have been already touched 
upon by my predecessors. It has been long known 
that the elements of the earth’s magnetic force were 
subject to certain regular and recurring changes, whose 
periods were respectively a day and a year, and which 
therefore were referred to the sun as their source. To 
these periodical changes Dr. Lament, of Munich, added 
another of ten years, the diurnal range of the mag¬ 
netic declination having lieen feund to pass from a 
maximum to a minimum, and back again in about that 
time. But besides these slow and regular changes, 
there are others of a different class, which recur at 
irregular intervals, and which are characterised by a 
large deviation of the magnetic elements from their 
normal state, and generally also by rapid fluctuation 
and change. These phenomena, called by Humboldt 
“ magnetic storms,” have been observed to occur simul¬ 
taneously in the most distant parts of the earth, and 
thus to indicate a cause operating upon the entire globe. 
But, casual as they seem, these effects are found to 
he subject^ to laws of their own Prof. Kreil was the 
first to discover that, at a given place, they recurred 
more frequently at certain hours of the day than at 
others; and that, consequently, in their mean effects 
they were subject to periodical laws, depending upon 
the hour at each station. The laws of this periodicity 
have been ably worked out by General Sabine in his 
discussion of the results of the British Colonial Obser¬ 
vatories ; and he lias added the important facts, that 
the same phenomena observe also the two other periods 
already noticed—namely, the annual and the decennial 
periods. He has further arrived at the very remark¬ 
able result, that the decennial magnetic period coin¬ 
cides, both in its duration and in its epochs of maxima 
and minima, with the decennial period observed l>y 
Schwabe in the solar spots; from which it is to lie 
inferred that the sun exercises a magnetic influence 
upon the earth dependent on the condition of its lumi¬ 
nous envelope. Wo arc thus in tho presence of two 
facts, which appear at first sight opposed—namely, the 
absolute simultanietv of magnetic disturbances at all 
parts of the earth, and their predominance at certain 
local horn’s at each place. General Sabine accounts 
for this apparent discrepancy by the circumstance that 
the hours of maximum disturbance are different for the 
different elements; so that there may be an abnormal 
condition of the magnetic force, operating at the same 
instant over the whole globe, but manifesting itself at 
one place chiefly in one element, and at another place 
in another. I would venture to suggest, as a subject 
of inquiry, whether the phenomena which have been 
hitherto grouped together as “occasional” effects may 
not possibly include two distinct classes of changes, 
obeying separate laws: one of them being strictly 
periodic, and constituting a part of the regular diurnal 
change; while the other is strictly abnormal, and 
simultaneous at all parts of the globe. Tf this be so, 
it would follow that we are not justified in sepa¬ 
rating the larger changes from tho rest, merely on the 
ground of their magnitude, and that a different analysis 
of the phenomenon is required. The eiferts liitlierto 
considered are all referable to the sun as their cause. 
Prof. Kreil discovered, however, that another body of 
onr system — namely, our own satellite—exerted an 
effect upon the magnetic needle, and that the magnetic 
declination underwent a small and very regular varia¬ 
tion, whose amount was dependent on the lunar hour- 
angle, and whose period was thefore a lunar day. This 
singular result was subsequently confirmed ’ by Mr. 
Broun in the discussion of the Makerstown Observa¬ 
tions ; and its laws have since been fully traced, for all 
the magnetic elements, by General Sabine, in the dis¬ 
cussion of the results obtained at the Colonial Magnetic 
Observatories. The foregoing facts bear closely upoa 
tho debated question of the causes of the magnetic 
variations. It has been usual to ascribe the periodical 
changes of the earth’s magnetic force to the thermic 
action of tho sun, operating either directly upon the 
magnetism of tho earth, or affecting it indirectly by the 
induction of the thermo-electric currents. Here, how¬ 
ever, we have a distinct case of magnetic action, unac¬ 
companied by heat; and the question Is naturally sug¬ 
gested, whether tho larger diurnal change may not 
also be independent of temperature. The most im¬ 
portant fact, in it3 bearing upon this question, is the 
existence of an annual inequality in the diurnal varia¬ 
tion, dependent on the sun’s declination, which has 
been recently pointed out by General Sabine. If we 
deduct tho ordinate of the curve which represents the 
mean diurnal variation for the entire year from those 
for the summer and winter half-yearly curves respec¬ 
tively, the differences are fonnd to be equal, and oppo¬ 
site ; and the curves themselves, consequently, are 
similar, but oppositely placed , with respect to the 
axses of abscissa*. Prom this, General Sabine draws 
the inference, that tho diurnal variation is a direct 
effect of solar action, and not a result of its thermic 
agency. 
The most important step which has been recently 
taken in this conntry to advance the science of Me¬ 
teorology has been the formation of a department con¬ 
nected with the Board of Trade, for the collection and 
discussion of meteorological observations made at sea. 
The practical results of a similar undertaking in the 
United States are now well known. The charts and 
sailing directions published by Lieutenant Maury have i 
enabled navigators to shorten their passages, in many 
cases by one-fourth of the time, and in some even to a 
greater extent. The commercial importance of such a 
result could not fail to attract general attention; and 
accordingly when the United States Government invited 
other maritime nations to co-operate in the undertaking, 
the invitation was cordially accepted. A eohference 
was held at Brussels in 1853, at which meteorologists 
deputed by tliose powers attended; and a Report was 
made recommending the conrse to he pursued in a 
general system of marine meteorological observations. 
This Report was laid before the British Parliament 
soon after, and a sum of money was voted for the neces¬ 
sary expenditure. The British Association undertook 
to supply verified instruments by means of its Obser¬ 
vatory at Kew; and the Royal Society, in consultation 
with the most eminent meteorologists of Europe and 
America, addressed an able Report to the Board of 
Trade, in which the objects to he attended to, so as to 
render the system of observation most available for 
science, were clearly set forth. With this co-operation 
on the part of the two leading scientific societies, the 
establishment was soon organized. It was placed under 
the direction of a distinguished naval officer, Admiral 
Fitz-Roy, and in the beginning of 1855 it was in opera¬ 
tion, Agents were established at the principal ports 
for the supply of instruments, books, and instructions; 
and there are now more than 200 British ships so fur¬ 
nished, whose officers have undertaken to make and 
record the required observations, and to transmit them 
from time to time to the department. The observations 
are tabulated, by collecting together, in separate books, 
those of each month, corresponding to geographical 
spates bounded by meridian and parallels 10 degrees 
apart. At the present time 700 months of logs have 
been received from nearly 100 merchant ships and are 
in process of tabulation. Holland is taking similar 
steps ; and the Meteorological Institute of that country, 
under the direction of Mr. Buys Bellet, has already 
