« ZurückWeiter »
head be immediately cut off to make it bleed, when it may be plucked and dressed immediately. This quantity of electricity is supposed sufficient for a turkey of ten pounds weight, and perhaps for a lamb. Experience alone will inform us of the requisite proportions for animals of different forms and ages. Probably not less will be required to render a small bird, which is very old, tender, than for a larger one, which is young. It is easy to furnish the requisite quantity of electricity, by employing a greater or less number of jars. As six jars, however, discharged at once, are capable of giving a very violent shock, the operator must be very circumspect, lest he should happen to make the experiment on his own flesh, instead of that of the fowl.
TO M. DUBOURG.
In Answer to some Queries concerning the Choice of
Glass for the Leyden Experiment.
London, 1 June, 1773.
I wish, with you, that some chemist (who should, if possible, be at the same time an electrician) would, in pursuance of the excellent hints contained in your letter, undertake to work upon glass with the view you have recommended. By means of a perfect knowledge of this substance, with respect to its electrical qualities, we might proceed with more certainty, as well in making our own experiments, as in repeating those which have been made by others in different countries, which, I believe, have frequently been attended with
different success on account of differences in the glass employed, thence occasioning frequent misunderstandings and contrariety of opinions.
There is another circumstance much to be desired with respect to glass, and that is, that it should not be subject to break when highly charged in the Leyden experiment. I have known eight jars broken out of twenty, and, at another time, twelve out of thirty-five. A similar loss would greatly discourage electricians desirous of accumulating a great power for certain experiments. We have never been able "hitherto to account for the cause of such misfortunes. The first idea which occurs is, that the positive electricity, being accumulated on one side of the glass, rushes violently through it, in order to supply the deficiency on the other side and to restore the equilibrium. This, however, I cannot conceive to be the true reason, when I consider, that, a great number of jars being united, so as to be charged and discharged at the same time, the breaking of a single jar will discharge the whole; for, if the accident proceeded from the weakness of the glass, it is not probable, that eight of them should be precisely of the same degree of weakness, as to break every one at the same instant, it being more likely, that the weakest should break first, and, by breaking, secure the rest; and again, when it is necessary to produce a certain effect, by means of the whole charge passing through a determined circle, (as, for instance, to melt a small wire,) if the charge, instead of passing in this circle, rushed through the sides of the jars, the intended effect would not be produced; which, however is contrary to fact. For these reasons, I suspect, that there is, in the substance of the glass, either some little globules of air, or some portions of unvitrified sand or salt, into which a quantity of the electric fluid may be forced
during the charge, and there retained till the general discharge; and that the force being suddenly withdrawn, the elasticity of the fluid acts upon the glass in which it is enclosed, not being able to escape hastily without breaking the glass. I offer this only as a conjecture, which I leave to others to examine.
The globe which I had that could not be excited, though it was from the same glass-house which furnished the other excellent globes in my possession, was not of the same frit. The glass which was usually manufactured there, was rather of the green kind, and chiefly intended for drinking-glasses and bottles; but, the proprietors being desirous of attempting a trial of white glass, the globe in question was of this frit. The glass not being of a perfect white, the proprietors were dissatisfied with it, and abandoned their project. I suspected, that too great a quantity of salt was admitted into the composition ; but I am no judge of these matters.
&c.; and M. Le Roy, of the Academy of Sciences at Paris, has lately given a Memoir recommending the use of them in that kingdom, which has been long opposed and obstructed by Abbé Nollet. Of the Duke of Tuscany he says, “Ce prince, qui ne connoît pas de délassement plus agréable des soins pénibles du gouvernement, que l'étude de la physique, a ordonné, l'année dernière, qu'on établît de ces barres au-dessus de tous les magasins à poudre de ses Etats; on dit que la république de Venise a donné les mêmes ordres.”
QUERIES ON ELECTRICITY, FROM DR. INGENHOUSZ ; *
WITH ANSWERS BY DR. FRANKLIN.
QUESTION I. If the electrical fluid is truly accumulated on the inside of a Leyden phial, and expelled in the same proportion from the other side, why are the particles of glass not all thrown outwards, when the phial being overcharged breaks, or is perforated by a spontaneous explosion ?
By the circumstances that have appeared to me, in all the jars that I have seen perforated at the time of their explosion, I have imagined that the charge did not pass by those perforations. Several single jars, that
* An eminent physician and chemist, born at Breda in 1730. He passed a large part of his life in England, where he died, September 7th, 1799.- EDITOR.
have broke while I was charging them, have shown, besides the perforation in the body, a trace on both sides of the neck, where the polish of the glass was taken off the breadth of a straw; which proved that great part at least of the charge, probably all, had passed over that trace. I was once present at the discharge of a battery containing thirty jars, of which eight were perforated and spoilt at the time of the discharge; yet the effect of the charge on the bodies upon which it was intended to operate, did not appear to be diminished. Another time I was present when twelve out of twenty jars were broken at the time of the discharge; yet the effect of the charge, which passed in the regular circuit, was the same as it would have been if they had remained whole. Were those perforations an effect of the charge within the jar forcing itself through the glass to get at the outside, other difficulties would arise and demand explanation. 1. How it happens, that in eight bottles, and in twelve, the strength to bear a strong charge should be so equal, that no one of them would break before the rest, and thereby save his fellows; but all should burst at the same instant. 2. How it happens, that they bear the force of the great charge till the instant that an easier means of discharge is offered them, which they make use of, and yet the fluid breaks through at the same time.
My conjecture is, that there has been, in the place , where the rupture happens, some defect in the glass, some grain of sand perhaps, or some little bubble in the substance nearly void, where, during the charging of the jar, the electric fluid is forced in and confined till the pressure is suddenly taken off by the discharge, when, not being able to escape so quickly, it bursts its way out by its elastic force. Hence all the ruptures