4 SEVENTH REPORT—1837. 
tury, the bare fact of there being any difference whatsoever in 
the intensity of the magnetic force in different parts of the 
earth was unattested by a single published observation. The 
maps attached to this memoir exhibit the progress which inves- 
tigation has made in the years that have since elapsed. They 
contain 753 distinct determinations, at 670 stations widely dis- 
tributed over the earth’s surface; leaving, it is true, much still 
to be desired ;—but in what has been accomplished, leading 
to conclusions so remarkable, in regard to the phenomena of 
magnetism, on the largest scale presented to us by nature, as 
to stimulate greatly to more extensive research. 
I have sought to embody in this report on the variations of 
the magnetic intensity, all the materials which have been ob- 
tained by the labours of observers of all nations, in all parts of 
the world ;—to present them in the form best fitted to add to 
our knowledge ;—and to call attention to the general conclu- 
sions, to which we are conducted by an attentive consideration 
of the facts of observation, when thus brought together in one 
view. A large portion of these determinations are here pub- 
lished for the first time. The observations of Capt. de Frey- 
cinet, Capt. King, Mr. Douglas, Capt. Fitz Roy, Capt. Ross, 
and Major Estcourt are wholly new, the original observations 
having been recently communicated to me by the respective 
observers, and calculated and arranged by me. Messrs. 
Hansteen and Due’s Siberian observations, and M. Erman’s in 
the Pacific and Atlantic oceans, have been furnished to me by 
the liberality of those gentlemen, calculated as they appear 
here. Of the results previously published, the greater number 
are collected from different foreign works which have little cir- 
culation in this country; and some of these, as well as a part of 
my own observations published in this country several years 
ago, have required additional calculations, for the purpose of 
bringing them into the general comparison. 
I have divided the report into three sections ; the first, con- 
taining a condensed historical notice of each of the several series 
of observations, by which our knowledge of the magnetic in- 
tensity has been progressively advanced; the second, comprising 
the whole of the results, classed according to the values of the 
intensity, and arranged in a tabular form; and the third, con- 
taining asummary of the principal general conclusions in regard 
to the system of terrestrial magnetism, which are deducible 
from the facts thus collected. 
I have endeavoured to confine the historical notices in the 
first section within the narrowest limits compatible with the pri- 
mary object, that of including in each notice all the circum- 
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