356 
GENERAL SIR EDWARD SABINE ON TERRESTRIAL MAGNETISM. 
confidence. The impression produced on my own mind is the probability of a reversal 
having taken place in the direction of the secular change at some time in the interval 
between 1818 and 1860, whereby the direction of the change which had been “increasing 
Easterly” or “decreasing Westerly” in the space between Melville Island and Baffin’s 
Bay became “decreasing Easterly” or “ increasing Westerly ” in the same localities. 
The epoch of a change of this description may indeed be supposed to have synchronized 
approximately with the reversal in the direction of the secular change of the Declination 
and of the Inclination which is now generally believed to have taken place in or about 
the same meridians in Canada* and the United States; and it may be right to connect 
both with the easterly progression of the phenomena in North-eastern Asia , attesting 
the approach of the present Asiatic point of maximum Force to the American continent. 
These, however, are matters which may be safely left to the elucidation they may receive 
from future researches in the same or in approximate localities ; towards which the best 
service which can be at present rendered is the assemblage in groups, approximate in 
time and locality, of the facts which we now possess. Such an assemblage will be found 
at the close of Zone 8. 
Amongst the Magnetic Determinations made at sea , the fine series of Professor 
Adolph Erman in the corvette ‘ Krotkoi ’ (commencing at Kamtschatka in October 
1829, passing round Cape Horn, and terminating at St. Petersburg in October 1830) 
may claim a special notice, both on account of the extent of oceanic surface which it 
covers, and the regard given to all the incidental circumstances which are conducive to 
the accuracy of conclusions obtained on board ship. The results are found in his well- 
known publication, the ‘ Beise um die Erde’ (Berlin, 1841). I have found nothing either 
to alter or to add in the Declinations and Inclinations recorded in that volume (excepting 
the introduction of the secular corrections furnished by himself, of which I have already 
spoken) ; in regard, however, to the values assigned to the magnetic Force , I have availed 
myself of the observations made by Professor Erman, in the return voyage to Europe, 
at Portsmouth in August 1830, to bring the whole series of his sea observations of the 
Force, of which those at Portsmouth formed a part, into direct comparison with the 
values assigned by British observers. The Magnetic Survey of the British Islands 
(Phil. Trans. 1870, Art. XIV.) assigns as the value of the Total Force at the “ Mother- 
* There is direct evidence of a reversal in the direction of the secular change in the Declination having 
taken place at York Fort, from Easterly increasing to Easterly diminishing, about the date 1842, in the 
record of three careful observers, Franklin, Leeroy, and Blakiston (Proceedings of the Royal Society, 
January 7, 1858). 0 ( 
The observations of Franklin in September 1819 gave 6 00 E. 
Those of Lefroy in July 1843 gave 9 25 E. 
Those of Blakiston in August 1857 gave 7 37 E. 
The reversal in the direction of the secular change of the Declination possibly took place at York Fort, as 
it may have done at Toronto, somewhat earlier than 1842-5 ; it is impossible to speak with certainty in regard 
to the precise epoch of the reversal at Toronto, because the Magnetic Observatory at that station was only esta- 
blished in 1840. 
