Accumulation of the electrical Fire proved to be in the electrified Glass.—Effect of Lightning on the Needle of Compasses, explained.—Gunpowder fired by the electric Flame.
Philadelphia, July 27, 1750.
Sir,
Mr. Watson, I believe, wrote his Observations on my last paper in haste, without having first well considered the experiments related §. 17 , 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 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.
B. FRANKLIN.
TO C. C[58]. ESQ. AT NEW-YORK, COMMUNICATED TO MR. COLLINSON.
