(888.) 
Variations 
of mag- 
netic ele- 
ments. 
—1. Seen- 
lar. 
(889.) 
—2. Diur- 
nal. 
(890.) 
—83. Irre- 
gular. 
(891.) 
(892.) 
992 
careful observations made in the Alps and Pyrenees 
with Hansteen’s apparatus, and studiously corrected 
for temperature, the present writer has found a 
diminution of one-thousandth part in the horizontal 
intensity for avertical ascent of about 3000 feet." 
Such are the general features of the distribution of 
the magnetic force upon the surface of the globe. But 
from an early period the magnetic elements for the 
same place have been known to be variable. Such 
deviations from constancy are either—1. Secular; 2. 
Periodic ; 3. Irregular. All the three magnetic ele- 
ments (Variation, Dip, and Intensity) probably par- 
take of these changes. The westerly Variation or De- 
clination had till 1818 been increasing in Europe since 
the earliest observations. This results from a com- 
plicated movement of the line of No Variation and 
its companion curves. While their common centre 
or pole in North America has been slowly advancing 
towards the East, a considerable portion of the sys- 
tem of curves in this quarter of the globe has been 
proceeding in a south-westerly direction nearly in a 
line joining Spain with South America, thus produc- 
ing a complicated rotatory motion of the lines of Va- 
riation, of which the first effect was to extinguish the 
singular loop in the curve of No Declination (in- 
cluding a space of easterly declination) which is 
shown in M. Hansteen’s chart for 1600 to have 
occupied a large part of Western Europe.? About 
1818 the needle began to retrograde towards the 
east in this part of Europe. The dip has been dimi- 
nishing in Europe since the earliest observations. 
Graham discovered the Diurnal Variation of the 
Compass. It occurs in a reversed direction in the 
southern hemisphere, Near the equator (as at St 
Helena) the needle partakes at one season of the 
northern character, at another of the southern, de- 
pending on the position of the sun. 
To Baron Humboldt and to Arago we are prin- 
cipally indebted for a knowledge of great and capri- 
cious fluctuations of the magnetic elements occurring 
simultaneously over vast regions of the earth. These 
have been called magnetic storms,’ They are often 
connected with auroral appearances. 
Next to Professor Hansteen, science is mainly in- 
debted for the recent great extension of our know- 
ledge of the facts and laws of terrestrial magnetism 
to two illustrious German philosophers, Baron Alex- 
ander von Humboldt and the late Professor Gauss. 
The name of AtexanpeR von Humsoxpr is as 
MATHEMATICAL AND PHYSICAL SCIENCE. 
[Diss. VI. 
widely known as science is cultivated. The ardour Baron 
of his love of nature, the comprehensive interest which Alexander 
von Hum- 
he takes in every department of knowledge, and the pojat, 
generosity of his disposition, in combination with the 
fortunate accidents of an unusually vigorous constitu- 
tion, and an eminent social position, have combined 
to place him in the foremost rank of natural philoso- 
hers. 
: He was born on the 14th September 1769, and 
consequently is now (1856) in his 87th year. 
was a pupil of Werner in 1791, and devoted consi- 
derable attention to metallurgy. An early longing 
for foreign travel seems to have foreshadowed his 
future career, but political circumstances were, to- 
wards the close of the last century, eminently un- 
favourable to its accomplishment. His celebrated 
journey to Southern and Central America (under- 
taken after the failure of several other schemes) lasted 
from June 1799 until August 1804. We may, per- 
haps, be allowed to regret that an impression of the 
duty of presenting to the public the results of that 
interesting journey in their most complete form 
should have absorbed the leisure of so many of his 
most vigorous years, and should have withheld him 
from other and still more important enterprizes. 
From 1808 to 1826 Baron Humboldt resided mainly 
in Paris, in the most intimate companionship with 
Arago, who, though much his junior, has predeceased 
him. He then took up his residence at Berlin, in 
compliance with the wish of the King of Prussia, and 
he soon after delivered there a course of public lec- 
tures on Physical Geography which formed the basis 
of his remarkable work entitled Kosmos, the compo- 
sition of which has formed the chief occupation of his 
vigorous old age. In 1829 he madea rapid but in- 
teresting journey into Asiatic Russia, important in 
its results, yet imperfectly carrying out the ardent 
aspiration of his early years to unfold the marvellous 
physical peculiarities of the Eastern continent. 
Baron Humboldt has contributed more to Physical 
and encouragement which he has given to innumer- 
able travellers and naturalists. His career seems to 
have been more closely modelled upon that of De 
Saussure than of any other of his contemporaries or 
predecessors. Those branches of Physical Geography 
which admit of numerical treatment seem most con- 
genial to him; and he has left more of the impress ~ 
of his personal influence upon the sciences of Meteor- 
1 Edinburgh Transactions, vol. xiii. 
2 M. Arago 
gives, no doubt, an erroneous impression in stating that the westerly movement of the line of No Declination has 
carried it in 200 years from Paris to Philadelphia. Yet I cannot subscribe to the opinion of his able commentator that the 
Loop of No Declination which passed over Europe in the seventeenth century moved eastwards, and may still be traced in Asia 
—(British Association, Fifth Report, p. 63; Arago’s Meteorological Essays, translated, p. 330). I conceive that, as stated in the 
text, the loop moved south-westwards, became successively an oval and a singular point, and was finally worked out previously 
to 1700. 
* In September 1841 a remarkable simultaneous disturbance took place in Canada, Scotland, the Cape of Good Hope, and New 
South Wales, Such occurrences are now known to be very common. 
_ (894: 
Geography than any other man now living ; and that, ae 
not only by his individual efforts, but by the direction Geography 
(893.) 
His early 
= history and 
travels. 
