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GENERAL SIR EDWARD SABINE ON TERRESTRIAL MAGNETISM. 
lished by MM. Gauss and Weber, in the ‘Atlas des Erdmagnetismus ’ (Leipsic, 1840) ; 
and 2°, in the Tables and Maps of the present paper. For the values of the magnetic 
Force, which in the Atlas of MM. Gauss and Weber are expressed in the Arbitrary 
Scale, of which the fundamental value is F372, or (as written by M. Gauss) 1372 = the 
Force in London in 1836, 1 have substituted the Absolute Values, corresponding to 1028 
as the Absolute Force in London at the same Epoch, in the scale which was originally 
adopted in conformity with the Report of the Committee of Physics of the Royal Society, 
1840, page 21 *. In all the three Elements there are some blanks in the columns derived 
from the data in the present paper, owing to observations being either wanting or insuffi- 
cient in those localities. Some of these blanks, viz. those in the vicinity of the Pole of 
the Earth, it will, probably, never be possible to till up ; but many of those in Lats. 40° 
and 45° may probably be supplied, when the evidence which this paper affords is sup- 
plemented by results South of 40° of N. Latitude, which are now in hand. 
* The Section of the Report in which the Scale is premised, in which the values of the magnetic Force 
should thenceforward he expressed, generally known as the “ Scale of British Units,” was from the pen of its 
Chairman, the late Sir John Herschel, Bart. ; the Scale is thus defined by him : — “ The number thus obtained, 
for the Force of the Earth’s Magnetism, expresses the Ratio which that Force bears to the Unit of Force-, the 
Unit of Force being that which acting on the Unit of Mass, through the Unit of Time, generates in it the unit 
of Velocity. For the unit of Mass we take, a grain ; for the unit of Time, a second ; and if a Foot he taken as 
the unit of Space, the unit of Velocity will be that of one foot per second.” 
