I have received your favour of the 24th of January past, inclosing
an extract from your letter to Mr. Collinson, and ****'s letter to
yourself, which I have read with a great deal of pleasure, and am
much obliged to you for. Your extract confirms a correction Mr.
Kinnersley made a few days ago, of a mistake I was under respecting
the polarity given to needles by the electrical fire, "that the end
which receives the fire always points north;" and, "that the needle
being situated east and west, will not have a polar direction." You
find, however, the polarity strongest when the needle is shocked
lying north and south; weakest when lying east and west; which makes
it probable that the communicated magnetism is less, as the needle
varies from a north and south situation. As to the needle of Captain
Waddel's compass, if its polarity was reversed by the lightning,
the effect of lightning and electricity, in regard of that, seems
dissimilar; for a magnetic needle in a north and south situation (as
the compass needle was) instead of having its power reversed, or even
diminished, would have it confirmed or increased by the electric
fire. But perhaps the lightning communicated to some nails in the
binnacle (where the compass is placed) the magnetic virtue, which
might disturb the compass.
This I have heard was the case; if so, the seeming dissimilarity
vanishes: but this remarkable circumstance (if it took place) I
should think would not be omitted in Captain Waddel's account.
I am very much pleased that the explication I sent you, of the
crooked direction of lightning, meets with your approbation.
As to your supposition about the source of lightning, the luminous
appearance of the sea in the night, and the similitude between the
friction of the particles of salt and water, as you considered them
in their original separate state, and the friction of the globe and
cushion, very naturally led you to the ocean, as the grand source of
lightning: but the activity of lightning, or the electric element,
and the fitness of water to conduct it, together with the experiments
you mention of salt and water, seem to make against it, and to
prepare the way for some other hypothesis. Accordingly you propose
a new one, which is very curious, and not so liable, I think, to
objections as the former. But there is not as yet, I believe, a
sufficient variety of experiments to establish any theory, though
this seems the most hopeful of any I have heard of.
The effect which the discharge of your four glass jars had upon a
fine wire, tied between two strips of glass, puts me in mind of a
very similar one of lightning, that I observed at New-York, October,
1750, a few days after I left Philadelphia. In company with a number
of gentlemen, I went to take a view of the city from the Dutch
church steeple, in which is a clock about twenty or twenty-five feet
below the bell. From the clock went a wire through two floors, to
the clock-hammer near the bell, the holes in the floor for the wire
being perhaps about a quarter of an inch diameter. We were told, that
in the spring of 1750, the lightning struck the clock hammer, and
descended along the wire to the clock, melting in its way several
spots of the wire, from three to nine inches long, through one-third
of its substance, till coming within a few feet of the lower end, it
melted the wire quite through, in several places, so that it fell
down in several pieces; which spots and pieces we saw. When it got to
the end of the wire, it flew off to the hinge of a door, shattered
the door, and dissipated. In its passage through the holes of the
floors it did not do the least damage, which evidences that wire is a
good conductor of lightning (as it is of electricity) provided it be
substantial enough, and might, in this case, had it been continued to
the earth, have conducted it without damaging the building.[74]
Your information about your globe's raising the electric fire in
greater quantities, by means of a wire extended from the cushion to
the earth, will enable me, I hope, to remedy a great inconvenience
I have been under, to collect the fire with the electrifying glass
I use, which is fixed in a very dry room, three stories from the
ground. When you send your meteorological observations to ****, I
hope I shall have the pleasure of seeing them.