Mr. Watson, I believe, wrote his Observations on my last paper
in haste, without having first well considered the experiments
related §. 17[56], which still appear to me decisive in the
question,--_Whether the accumulation of the electrical fire be in the
electrified glass, or in the non-electric matter connected with the
glass?_ and to demonstrate that it is really in the glass.
As to the experiment that ingenious gentleman mentions, and which he
thinks conclusive on the other side, I persuade myself he will change
his opinion of it, when he considers, that as one person applying
the wire of the charged bottle to warm spirits, in a spoon held by
another person, both standing on the floor, will fire the spirits,
and yet such firing will not determine whether the accumulation
was in the glass or the non-electric; so the placing another person
between them, standing on wax, with a bason in his hand, into which
the water from the phial is poured, _while he at the instant of
pouring_ presents a finger of his other hand to the spirits, does not
at all alter the case; the stream from the phial, the side of the
bason, with the arms and body of the person on the wax, being all
together but as one long wire, reaching from the internal surface of
the phial to the spirits.
_June 29, 1751._ In Capt. Waddell's account of the effects of
lightning on his ship, I could not but take notice of the large
comazants (as he calls them) that settled on the spintles at the
top-mast heads, and burnt like very large torches (before the
stroke.) According to my opinion, the electrical fire was then
drawing off, as by points, from the cloud; the largeness of the flame
betokening the great quantity of electricity in the cloud: and had
there been a good wire communication from the spintle heads to the
sea, that could have conducted more freely than tarred ropes, or
masts of turpentine wood, I imagine there would either have been no
stroke, or, if a stroke, the wire would have conducted it all into
the sea without damage to the ship.
His compasses lost the virtue of the load-stone, or the poles were
reversed; the north point turning to the south.--By electricity we
have (_here_ at _Philadelphia_) frequently given polarity to needles,
and reversed it at pleasure. Mr. Wilson, at London, tried it on too
large masses, and with too small force.
A shock from four large glass jars, sent through a fine
sewing-needle, gives it polarity, and it will traverse when laid
on water.--If the needle, when struck, lies east and west, the end
entered by the electric blast points north.--If it lies north and
south, the end that lay towards the north will continue to point
north when placed on water, whether the fire entered at that end, or
at the contrary end.
The polarity given is strongest when the needle is struck lying north
and south, weakest when lying east and west; perhaps if the force was
still greater, the south end, entered by the fire (when the needle
lies north and south) might become the north, otherwise it puzzles us
to account for the inverting of compasses by lightning; since their
needles must always be found in that situation, and by our little
experiments, whether the blast entered the north and went out at the
south end of the needle, or the contrary, still the end that lay to
the north should continue to point north.
In these experiments the ends of the needles are sometimes finely
blued like a watch-spring by the electric flame.--This colour given
by the flash from two jars only, will wipe off, but four jars fix
it, and frequently melt the needles. I send you some that have had
their heads and points melted off by our mimic lightning; and a pin
that had its point melted off, and some part of its head and neck
run. Sometimes the surface on the body of the needle is also run,
and appears blistered when examined by a magnifying glass: the jars
I make use off hold seven or eight gallons, and are coated and lined
with tin foil; each of them takes a thousand turns[57] of a globe
nine inches diameter to charge it.
I send you two specimens of tin-foil melted between glass, by the
force of two jars only.
I have not heard that any of your European electricians have ever
been able to fire gun-powder by the electric flame. We do it here
in this manner:--A small cartridge is filled with dry powder, hard
rammed, so as to bruise some of the grains; two pointed wires are
then thrust in, one at each end, the points approaching each other in
the middle of the cartridge till within the distance of half an inch;
then, the cartridge being placed in the circuit, when the four jars
are discharged, the electric flame leaping from the point of one wire
to the point of the other, within the cartridge amongst the powder,
_fires it_, and the explosion of the powder is at the same instant
with the crack of the discharge.
Your's, &c.