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and form for a compass needle. 
capability of receiving magnetism, though not apparently 
differing in any other respect. 
That polishing the needle has no effect on its magnetism. 
That the best mode of communicating magnetism to a 
needle, appears to be by placing it in the magnetic meridian, 
joining the opposite poles of a pair of bar magnets (the mag- 
nets being in the same line), and laying the magnets so joined* 
flat upon the needle with their poles upon its centre ; then 
having elevated the distant extremities of the magnets, so 
that they may form an angle of about two or three degrees 
with the needle, they are to be drawn from the centre of 
the needle to the extremities, carefully preserving the same 
inclination, and having joined the poles of the magnets at a 
distance from the needle, the operation is to be repeated ten 
or twelve times on each surface. 
That in needles from 5 to 8 inches in length, their weights 
being equal, the directive forces are nearly as the lengths. 
That the directive force does not depend upon extent of 
surface, but in needles of nearly the same length and form, 
is as the mass. 
That the deviation of a compass needle occasioned by the 
attraction of soft iron, depends, as Mr. Barlow has advanced, 
on extent of surface, and is wholly independent of the mass, 
except a certain thickness of the iron, amounting to about 
two tenths of an inch, which is requisite for the complete 
developement of its attractive energy. 
MDCCCXXI. 
S 
