Makers of ElectricityWalsh, James J. (James Joseph)
History
Makers of Electricity
Walsh, James J. (James Joseph)
Electricity -- Biography
The same illustration shows another experiment which Norman made in
order to determine whether the earth exerts a force of translation on a
magnet, in virtue of which the magnet would tend to move bodily toward
the pole. For this purpose, he floated a magnetized piece of steel wire
on the surface of the water and noticed that, wherever placed, it merely
swung round into the magnetic meridian without showing any tendency to
move northward or southward toward the rim of the vessel. Hartmann, who
observed the declination of the needle on land as stated on p. 26,
appears also to have been the first to notice magnetic inclination.
Having balanced a steel needle with great precision, he found that,
after magnetization, it did not remain horizontal, the north-seeking end
invariably dipping through an angle of 9°. The smallness of the angle in
this experiment was due to the fact that the needle used by the
Nuremberg Vicar could move only in a horizontal plane, whereas Norman's
was free to move in a vertical circle. Had Hartmann used such a device,
he would have obtained more than 60° for the dip instead of the 9° which
he records.
[Illustration: FIG. 6 Norman's illustration of magnetic dip]
As already remarked, the letter in which Hartmann consigns these capital
observations was written in 1544, but was not published until the third
decade of the nineteenth century, so that Norman has clearly the full
merit of independent discovery.
In the directions which Norman gives for making observations of dip, he
states explicitly that the instrument must be adjusted "duley according
to the variation of the place," which means that the plane of the circle
must be turned into what was called after his time "the magnetic
meridian."
The discovery of magnetic dip led Norman to discard the view generally
held in his time, which placed the controlling influence of the
compass-needle in far-off celestial space; for he says that the _poynt
respective_ which the magnet indicates, but to which it is not bodily
drawn, is not in the heavens above, but in the earth itself. His words
are: "And by the declining of the needle is also proved that the poynt
respective is rather in the earth than in the heavens, as some have
imagined; and the greatest reason why they so thought, as I judge, was
because they were never acquainted with this declining in the needle."
Here we have a radical departure from the scientific creed of the time,
a notable advance in scientific theory, an entirely new philosophy
founded by Norman, the compass-maker, and greatly developed twenty-four
years later by his fellow-citizen, Gilbert, the physician.
[Illustration: FIG. 7 Gilbert's _orb of virtue_, 1600]
Public-domain text, read in full here on John Shaqi.
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