I am glad to learn, by your favour of the 21st past, that Mr.
Kinnersley's lectures have been acceptable to the gentlemen of
Boston, and are like to prove serviceable to himself.
I thank you for the countenance and encouragement you have so kindly
afforded my fellow-citizen.
I send you enclosed an extract of a letter containing the substance
of what I observed concerning the communication of magnetism to
needles by electricity. The minutes I took at the time of the
experiments are mislaid. I am very little acquainted with the nature
of magnetism. Dr. Gawin Knight, inventor of the steel magnets, has
wrote largely on that subject, but I have not yet had leisure to
peruse his writings with the attention necessary to become master of
his doctrine.
Your explication of the crooked direction of lightning appears to
me both ingenious and solid. When we can account as satisfactorily
for the electrification of clouds, I think that branch of natural
philosophy will be nearly complete.
The air, undoubtedly, obstructs the motion of the electric fluid. Dry
air prevents the dissipation of an electric atmosphere, the denser
the more, as in cold weather. I question whether such an atmosphere
can be retained by a body _in vacuo_. A common electrical phial
requires a non-electric communication from the wire to every part of
the charged glass; otherwise, being dry and clean, and filled with
air only, it charges slowly, and discharges gradually, by sparks,
without a shock: but, exhausted of air, the communication is so open
and free between the inserted wire and surface of the glass, that it
charges as readily, and shocks as smartly as if filled with water:
and I doubt not, but that in the experiment you propose, the sparks
would not only be near strait _in vacuo_, but strike at a greater
distance than in the open air, though perhaps there would not be a
loud explosion. As soon as I have a little leisure, I will make the
experiment, and send you the result.
My supposition, that the sea might possibly be the grand source
of lightning, arose from the common observation of its luminous
appearance in the night, on the least motion; an appearance never
observed in fresh water. Then I knew that the electric fluid may be
pumped up out of the earth, by the friction of a glass globe, on
a non-electric cushion; and that, notwithstanding the surprising
activity and swiftness of that fluid, and the non-electric
communication between all parts of the cushion and the earth, yet
quantities would be snatched up by the revolving surface of the
globe, thrown on the prime conductor, and dissipated in air. How
this was done, and why that subtle active spirit did not immediately
return again from the globe, into some part or other of the cushion,
and so into the earth, was difficult to conceive; but whether from
its being opposed by a current setting upwards to the cushion, or
from whatever other cause, that it did not so return was an evident
fact. Then I considered the separate particles of water as so many
hard spherules, capable of touching the salt only in points, and
imagined a particle of salt could therefore no more be wet by a
particle of water, than a globe by a cushion; that there might
therefore be such a friction between these originally constituent
particles of salt and water, as in a sea of globes and cushions; that
each particle of water on the surface might obtain from the common
mass, some particles of the universally diffused, much finer, and
more subtle electric fluid, and forming to itself an atmosphere of
those particles, be repelled from the then generally electrified
surface of the sea, and fly away with them into the air. I thought
too, that possibly the great mixture of particles electric _per se_,
in the ocean water, might, in some degree, impede the swift motion
and dissipation of the electric fluid, through it to the shores,
&c.--But having since found, that salt in the water of an electric
phial does not lessen the shock; and having endeavoured in vain to
produce that luminous appearance from a mixture of salt and water
agitated; and observed, that even the sea-water will not produce it
after some hours standing in a bottle; I suspect it to proceed from
some principle yet unknown to us (which I would gladly make some
experiments to discover, if I lived near the sea) and I grow more
doubtful of my former supposition, and more ready to allow weight to
that objection (drawn from the activity of the electric fluid, and
the readiness of water to conduct) which you have indeed stated with
great strength and clearness.
In the mean time, before we part with this hypothesis, let us think
what to substitute in its place. I have sometimes queried whether the
friction of the air, an electric _per se_, in violent winds, among
trees, and against the surface of the earth, might not pump up, as so
many glass globes, quantities of the electric fluid, which the rising
vapours might receive from the air, and retain in the clouds they
form? on which I should be glad to have your sentiments. An ingenious
friend of mine supposes the land-clouds more likely to be electrified
than the sea-clouds. I send his letter for your perusal, which please
to return me.
I have wrote nothing lately on electricity, nor observed any thing
new that is material, my time being much taken up with other affairs.
Yesterday I discharged four jars through a fine wire, tied up between
two strips of glass: the wire was in part melted, and the rest broke
into small pieces, from half an inch long, to half a quarter of an
inch. My globe raises the electric fire with greater ease, in much
greater quantities, by the means of a wire extended from the cushion,
to the iron pin of a pump handle behind my house, which communicates
by the pump spear with the water in the well.
By this post I send to ****, who is curious in that way, some
meteorological observations and conjectures, and desire him to
communicate them to you, as they may afford you some amusement, and
I know you will look over them with a candid eye. By throwing our
occasional thoughts on paper, we more readily discover the defects
of our opinions, or we digest them better and find new arguments to
support them. This I sometimes practise: but such pieces are fit only
to be seen by friends.