PROGRESS IN ELECTRICITY FROM GILBERT AND VON GUERICKE TO
We have seen how Gilbert, by his experiments with magnets, gave
an impetus to the study of magnetism and electricity. Gilbert
himself demonstrated some facts and advanced some theories, but
the system of general laws was to come later. T 18418h77s o this end the
discovery of electrical repulsion, as well as attraction, by Von
Guericke, with his sulphur ball, was a step forward; but
something like a century passed after Gilbert's beginning before
anything of much importance was done in the field of electricity.
In 1705, however, Francis Hauksbee began a series of experiments
that resulted in some startling demonstrations. For many years it
had been observed that a peculiar light was seen sometimes in the
mercurial barometer, but Hauksbee and the other scientific
investigators supposed the radiance to be due to the mercury in a
vacuum, brought about, perhaps, by some agitation. That this
light might have any connection with electricity did not, at
first, occur to Hauksbee any more than it had to his
predecessors. The problem that interested him was whether the
vacuum in the tube of the barometer was essential to the light;
and in experimenting to determine this, he invented his
"mercurial fountain." Having exhausted the air in a receiver
containing some mercury, he found that by allowing air to rush
through the mercury the metal became a jet thrown in all
directions against the sides of the vessel, making a great,
flaming shower, "like flashes of lightning," as he said. But it
seemed to him that there was a difference between this light and
the glow noted in the barometer. This was a bright light, whereas
the barometer light was only a glow. Pondering over this,
Hauksbee tried various experiments, revolving pieces of amber,
flint, steel, and other substances in his exhausted air-pump
receiver, with negative, or unsatisfactory, results. Finally, it
occurred to him to revolve an exhausted glass tube itself.
Mounting such a globe of glass on an axis so that it could be
revolved rapidly by a belt running on a large wheel, he found
that by holding his fingers against the whirling globe a purplish
glow appeared, giving sufficient light so that coarse print could
be read, and the walls of a dark room sensibly lightened several
feet away. As air was admitted to the globe the light gradually
diminished, and it seemed to him that this diminished glow was
very similar in appearance to the pale light seen in the
mercurial barometer. Could it be that it was the glass, and not
the mercury, that caused it? Going to a barometer he proceeded to
rub the glass above the column of mercury over the vacuum,
without disturbing the mercury, when, to his astonishment, the
same faint light, to all appearances identical with the glow seen
in the whirling globe, was produced.
Turning these demonstrations over in his mind, he recalled the
well-known fact that rubbed glass attracted bits of paper,
leaf-brass, and other light substances, and that this phenomenon
was supposed to be electrical. This led him finally to determine
the hitherto unsuspected fact, that the glow in the barometer was
electrical as was also the glow seen in his whirling globe.
Continuing his investigations, he soon discovered that solid
glass rods when rubbed produced the same effects as the tube. By
mere chance, happening to hold a rubbed tube to his cheek, he
felt the effect of electricity upon the skin like "a number of
fine, limber hairs," and this suggested to him that, since the
mysterious manifestation was so plain, it could be made to show
its effects upon various substances. Suspending some woollen
threads over the whirling glass cylinder, he found that as soon
as he touched the glass with his hands the threads, which were
waved about by the wind of the revolution, suddenly straightened
themselves in a peculiar manner, and stood in a radical position,
pointing to the axis of the cylinder.
Encouraged by these successes, he continued his experiments with
breathless expectancy, and soon made another important discovery,
that of "induction," although the real significance of this
discovery was not appreciated by him or, for that matter, by any
one else for several generations following. This discovery was
made by placing two revolving cylinders within an inch of each
other, one with the air exhausted and the other unexhausted.
Placing his hand on the unexhausted tube caused the light to
appear not only upon it, but on the other tube as well. A little
later he discovered that it is not necessary to whirl the
exhausted tube to produce this effect, but simply to place it in
close proximity to the other whirling cylinder.
These demonstrations of Hauksbee attracted wide attention and
gave an impetus to investigators in the field of electricity; but
still no great advance was made for something like a quarter of a
century. Possibly the energies of the scientists were exhausted
for the moment in exploring the new fields thrown open to
investigation by the colossal work of Newton.
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