GENERAL SIR EDWARD SABINE ON TERRESTRIAL MAGNETISM. 
355 
speaking, and excepting for very special reasons, the limit of about eighteen years before 
and after the mean epoch has not been departed from. In the large contribution made 
by Dr. Lamont, extending over a considerable portion of the European continent, I have 
only had to approve and to adopt his own estimate of secular change, and to apply the 
corrections accordingly. In a yet more extensive series, the well-known observations of 
MM. Hansteen, Erman, and Due, in the northern parts of Eastern Europe and of Asia, 
I have been aided by my early and valued friend Professor Adolph Erman, of Berlin, by 
whom the secular corrections of the three elements at the Land Stations of the three 
observers in Zones 3, 4, 5, and 6 have been supplied. I am also indebted to Professor 
Erman for the secular corrections applied to the observations of Wrangel and Anjou 
in North-eastern Asia. 
For a manuscript communication of a large portion of the Magnetic Determinations 
on the coasts and islands of the Asiatic Polar Sea, I have been indebted to the early and 
valued friendship of Admiral Count Lutke, himself a magnetician of no ordinary note, 
and who now holds the distinguished position of President of the Imperial Academy of 
Sciences at St. Petersburg. In assigning the Secular Corrections for these, and for 
other determinations around and eastward of the White Sea, I have been greatly aided 
by the publication (in the Russian language) of Captain Belavenetz, of the Russian 
Imperial Navy, Director of the Compass Observatory at Cronstadt. 
On the American continent, and until the Arctic Regions are approached, the obser- 
vations themselves furnish on the whole satisfactory materials for the assignment of 
secular change. The Inclination, indeed, appears to have been nearly stationary in 
Canada and in the northern states of America for some years before and after the mean 
epoch of 1842 - 5 — a conclusion which is confirmed by the records of the Toronto Obser- 
vatory, and is quite in accordance with the excellent observations and discussions in the 
volumes of the United States Coast Survey. But in Zones 6, 7, and 8 the American 
portions present more than ordinary difficulties in respect to secular change, — 
especially in the case of the Declination, in which element a satisfactory conclusion 
seemed especially desirable, as likely to possess a more than ordinary theoretical value, 
in addition to that attaching to it for the sake of corrections to the mean epoch. The 
observations are tolerably numerous, both in the earlier and in the later portions of the 
included time ; and it must also be said that the difficulty referred to is only partially 
due to the increased amount of probable error in the observations, incident to a region 
where the intensity of the Terrestrial Magnetic Force acting on the Declination Magnet 
is so greatly reduced. This latter inconvenience is one which it has in many cases been 
possible to counteract in some degree, by forming groups of results, with due regard to 
proximity in time and space ; but the intercomparison of such groups (so far as they 
might admit of iutercomparison), and the general and particular consideration of the 
data in various ways with a view to the derivation of secular change, have failed to 
enable me to derive conclusions in regard to the secular change which may have taken 
place in those localities between 1818 and I860 which I could put forward with sufficient 
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