[74] The wire mentioned in this account was re-placed by a small
brass chain. In the summer of 1763, the lightning again struck that
steeple, and from the clock-hammer near the bell, it pursued the
chain as it had before done the wire, went off to the same hinge,
and again shattered the same door. In its passage through the same
holes of the same floors, it did no damage to the floors, nor to the
building during the whole extent of the chain. But the chain itself
was destroyed, being partly scattered about in fragments of two or
three links melted and stuck together, and partly blown up or reduced
to smoke, and dissipated. [See an account of the same effect of
lightning on a wire at Newbury, p. 311.] The steeple, when repaired,
was guarded by an iron conductor, or rod, extending from the foot of
the vane-spindle down the outside of the building, into the earth.
The newspapers have mentioned, that in 1765, the lightning fell a
third time on the same steeple, and was safely conducted by the rod;
but the particulars are not come to hand.
_Proposal of an Experiment to measure the Time taken up by an
Electric Spark, in moving through any given Space. By J. A.[75]
Esq. of New-York._
Read at the Royal Society, Dec 26, 1756.
If I remember right, the Royal Society made one experiment to
discover the velocity of the electric fire, by a wire of about four
miles in length, supported by silk, and by turning it forwards and
backwards in a field, so that the beginning and end of the wire were
at only the distance of two people, the one holding the Leyden bottle
and the beginning of the wire, and the other holding the end of the
wire and touching the ring of the bottle; but by this experiment no
discovery was made, except that the velocity was extremely quick.
As water is a conductor as well as metals, it is to be considered
whether the velocity of the electric fire might not be discovered by
means of water; whether a river, or lake, or sea, may not be made
part of the circuit through which the electric fire passes? instead
of the circuit all of wire, as in the above experiment.
Whether in a river, lake, or sea, the electric fire will not
dissipate and not return to the bottle? or, will it proceed in strait
lines through the water the shortest courses possible back to the
bottle?
If the last, then suppose one brook that falls into Delaware doth
head very near to a brook that falls into Schuylkil, and let a wire
be stretched and supported as before, from the head of the one brook
to the head of the other, and let the one end communicate with the
water, and let one person stand in the other brook, holding the
Leyden bottle, and let another person hold that end of the wire not
in the water, and touch the ring of the bottle.--If the electric fire
will go as in the last question, then will it go down the one brook
to Delaware or Schuylkill, and down one of them to their meeting,
and up the other and the other brook; the time of its doing this
may possibly be observable, and the further upwards the brooks are
chosen, the more observable it would be.
Should this be not observable, then suppose the two brooks falling
into Sasquehana and Delaware, and proceeding as before, the electric
fire may, by that means, make a circuit round the North Cape of
Virginia, and go many hundreds of miles, and in doing that, it would
seem it must take some observable time.
If still no observable time is found in that experiment, then
suppose the brooks falling the one into the Ohio, and the other into
Sasquehana, or Potomack, in that the electric fire would have a
circuit of some thousands of miles to go down Ohio to Mississippi,
to the Bay of Mexico, round Florida, and round the South Cape of
Virginia; which, I think, would give some observable time, and
discover exactly the velocity.
But if the electric fire dissipates, or weakens in the water, as I
fear it does, these experiments will not answer.
_Answer to the foregoing_.
Read at the Royal Society, Dec. 25, 1756.
Suppose a tube of any length open at both ends, and containing a
moveable wire of just the same length, that fills its bore. If I
attempt to introduce the end of another wire into the same tube, it
must be done by pushing forward the wire it already contains; and the
instant I press and move one end of that wire, the other end is also
moved; and in introducing one inch of the same wire, I extrude, at
the same time, an inch of the first, from the other end of the tube.
If the tube be filled with water, and I inject an additional inch of
water at one end, I force out an equal quantity at the other, in the
very same instant.
And the water forced out at one end of the tube is not the very same
water that was forced in at the other end at the same time, it was
only in motion at the same time.
The long wire, made use of in the experiment to discover the velocity
of the electric fluid, is itself filled with what we call its natural
quantity of that fluid, before the hook of the Leyden bottle is
applied to one end of it.
The outside of the bottle being at the time of such application
in contact with the other end of the wire, the whole quantity of
electric fluid contained in the wire is, probably, put in motion at
once.
For at the instant the hook, connected with the inside of the bottle,
_gives out_; the coating, or outside of the bottle, _draws in_ a
portion of that fluid.
If such long wire contains precisely the quantity that the outside
of the bottle demands, the whole will move out of the wire to the
outside of the bottle, and the over quantity which the inside of the
bottle contained, being exactly equal, will flow into the wire, and
remain there, in the place of the quantity the wire had just parted
with to the outside of the bottle.
But if the wire be so long as that one-tenth (suppose) of its natural
quantity is sufficient to supply what the outside of the bottle
demands, in such case the outside will only receive what is contained
in one-tenth of the wire's length, from the end next to it; though
the whole will move so as to make room at the other end for an equal
quantity issuing, at the same time, from the inside of the bottle.
So that this experiment only shews the extreme facility with which
the electric fluid moves in metal; it can never determine the
velocity.
And, therefore, the proposed experiment (though well imagined, and
very ingenious) of sending the spark round through a vast length of
space, by the waters of Susquehannah, or Potowmack, and Ohio, would
not afford the satisfaction desired, though we could be sure that the
motion of the electric fluid would be in that tract, and not under
ground in the wet earth by the shortest way.