28. In order to this, let it first be considered,that we cannot, by any means we are yet acquainted with, force the electrical fluid thro' glass. I know it is commonly thought that it easily pervades glass, and the experiment of a feather suspended by a thread in a bottle hermetically sealed, yet moved by bringing a nibbed tube near the outside of the bottle, is alledged to prove it. But, if the electrical fluid so easily pervades glass, how does the vial becomecharged(as we term it) when we hold it in our hands? Would not the fire thrown in by the wire pass through to our hands, and so escape into the floor? Would not the bottle in that case be left just as we found it, uncharged, as we know a metal bottle so attempted to be charged would be? Indeed, if there be the least crack, the minutest solution of continuity in the glass, though it remains so tight that nothing else we know of will pass, yet the extremely subtile electrical fluid flies through such a crack with the greatest freedom, and such a bottle we know can never be charged: What then makes the difference between such a bottle and one that is sound, but this, that the fluid can pass through the one, and not through the other?[8]
29. It is true there is an experiment that at first sight would be apt to satisfy a slight observer, that the fire thrown into the bottle by the wire, does really pass thro'the glass. It is this: place the bottle on a glass stand, under the prime conductor; suspend a bullet by a chain from the prime conductor, till it comes within a quarter of an inch right over the wire of the bottle; place your knuckle on the glass stand, at just the same distance from the coating of the bottle, as the bullet is from its wire. Now let the globe be turned, and you see a spark strike from the bullet to the wire of the bottle, and the same instant you see and feel an exactly equal spark striking from the coating on your knuckle, and so on spark for spark. This looks as if the whole received by the bottle was again discharged from it. And yet the bottle by this means is charged![9]And therefore the fire that thus leaves the bottle, though the same in quantity, cannot be the very same fire that entered at the wire; for if it were, the bottle would remain uncharged.
30. If the fire that so leaves the bottle be not the same that is thrown in through the wire, it must be fire that subsisted in the bottle, (that is, in the glass of the bottle) before the operation began.
31. If so, there must be a great quantity in glass, because a great quantity is thus discharged even from very thin glass.
32. That this electrical fluid or fire is strongly attracted by glass, we know from the quickness and violence with which it is resumed by the part that had been deprived ofit, when there is an opportunity. And by this, that we cannot from a mass of glass draw a quantity of electrical fire, or electrify the whole massminus, as we can a mass of metal. We cannot lessen or increase its whole quantity, for the quantity it has it holds; and it has as much as it can hold. Its pores are filled with it as full as the mutual repellency of the particles will admit; and what is already in, refuses, or strongly repels, any additional quantity. Nor have we any way of moving the electrical fluid in glass, but one; that is, by covering part of the two surfaces of thin glass with non-electrics, and then throwing an additional quantity of this fluid on one surface, which spreading in the non-electric, and being bound by it to that surface, acts by its repelling force on the particles of the electrical fluid contained in the other surface, and drives them out of the glass into the non-electric on that side, from whence they are discharged, and then those added on the charged side can enter. But when this is done, there is no more in the glass, nor less than before, just as much having left it on one side as it received on the other.
33. I feel a want of terms here, and doubt much whether I shall be able to make this part intelligible. By the wordsurface, in this case, I do not mean mere length and breadth without thickness; but when I speak of the upper or under surface of a piece of glass, the outer or inner surface of the vial, I mean length, breadth, and half the thickness, and beg the favour of being so understood. Now, I suppose, that glass in its first principles, and in the Furnace, has no more of this electrical fluid than other common matter: That when it is blown, as it cools, and the particles of common fire leave it, its pores become a vacuum: That the component parts of glass are extremely small and fine, I guess from its never showing a rough face when it breaks, but always a polish; and from the smallness of its particles I suppose the pores between them must be exceeding small, which is the reason that Aqua-fortis, nor any other menstruum we have, can enter to separate them and dissolve the substance; nor is any fluid we know of, fine enough to enter, except common fire, and the electrical fluid. Now the departing fire leaving a vacuum, as aforesaid, between these pores, which air nor water are fine enough to enter and fill, the electrical fluid (which is every where ready in what we call the non-electrics, and in the non-electric Mixtures that are in the air,) is attracted in: yet does not become fixed with the substance of the glass, but subsists there as water in a porous stone, retained only by the attraction of the fixed parts, itself still loose and a fluid. But I suppose farther, that in the cooling of the glass, its texture becomes closest in the middle, and forms a kind of partition, in which the pores are so narrow, that the particles of the electrical fluid, which enter both surfaces at the same time, cannot go through, or pass and repass from one surface to the other, and so mix together; yet, though the particles of electrical fluid, imbibed by each surface, cannot themselvespass through to those of the other, their repellency can, and by this means they act on one another. The particles of the electrical fluid have a mutual repellency, but by the power of attraction in the glass they are condensed or forced nearer to each other. When the glass has received and, by its attraction, forced closer together so much of this electrified fluid, as that the power of attracting and condensing in the one, is equal to the power of expansion in the other, it can imbibe no more, and that remains its constant whole quantity; but each surface would receive more, if the repellency of what is in the opposite surface did not resist its entrance. The quantities of this fluid in each surface being equal, their repelling action on each other is equal; and therefore those of one surface cannot drive out those of the other: but, if a greater quantity is forced into one surface than the glass would naturally draw in; this increases the repelling power on that side, and overpowering the attraction on the other, drives out part of the fluid that had been imbibed by that surface, if there be any non-electric ready to receive it: such there is in all cases where glass is electrified to give a shock. The surface that has been thus emptied by having its electrical fluid driven out, resumes again an equal quantity with violence, as soon as the glass has an opportunity to discharge that over-quantity more than it could retain by attraction in its other surface, by the additional repellency of which the vacuum had been occasioned. For experimentsfavouring (if I may not say confirming) this hypothesis, I must, to avoid repetition, beg leave to refer you back to what is said of the electrical phial in my former papers.
34. Let us now see how it will account for several other appearances.—Glass, a body extremely elastic (and perhaps its elasticity may be owing in some degree to the subsisting of so great a quantity of this repelling fluid in its pores) must, when rubbed, have its rubbed surface somewhat stretched, or its solid parts drawn a little farther asunder, so that the vacancies in which the electrical fluid resides, become larger, affording room for more of that fluid, which is immediately attracted into it from the cushion or hand rubbing, they being supply'd from the common stock. But the instant the parts of the glass so open'd and fill'd have pass'd the friction, they close again, and force the additional quantity out upon the surface, where it must rest till that part comes round to the cushion again, unless some non electric (as the prime conductor) first presents to receive it.[10]But if the inside of the globe be lined with a non-electric, theadditional repellency of the electrical fluid, thus collected by friction on the rubb'd part of the globe's outer surface, drives an equal quantity out of the inner surface into that non-electric lining, which receiving it, and carrying it away from the rubb'd part into the common mass, through the axis of the globe and frame of the machine, the new collected electrical fluid can enter and remain in the outer surface, and none of it (or a very little) will be received by the prime conductor. As this charg'd part of the globe comes round to the cushion again, the outer surface delivers its overplus fire into the cushion, the opposite inner surface receiving at the same time an equal quantity from the floor. Every electrician knows that a globe wet within will afford little or no fire, but the reason has not before been attempted to be given, that I know of.
34. So if a tube lined with a[11]non-electric, be rubb'd, little or no fire is obtained from it. What is collected from the hand in the downward rubbing stroke, entering the pores of the glass, and driving an equal quantity out of the inner surface into the non-electric lining: and the hand in passing up to take a second stroke, takes out again what had been thrown into the outer surface, and then the inner surface receives back again what it had given to the non-electric lining. Thus the particles ofelectrical fluid belonging to the inside surface go in and out of their pores every stroke given to the tube. Put a wire into the tube, the inward end in contact with the non-electric lining, so it will represent theLeydenbottle. Let a second person touch the wire while you rub, and the fire driven out of the inward surface when you give the stroke, will pass through him into the common mass, and return through him when the inner surface resumes its quantity, and therefore this new kind ofLeydenbottle cannot so be charged. But thus it may: after every stroke, before you pass your hand up to make another, let the second person apply his finger to the wire, take the spark, and then withdraw his finger; and so on till he has drawn a number of sparks; thus will the inner surface be exhausted, and the outer surface charged; then wrap a sheet of gilt paper close round the outer surface, and grasping it in your hand you may receive a shock by applying the finger of the other hand to the wire: for now the vacant pores in the inner surface resume their quantity, and the overcharg'd pores in the outer surface discharge that overplus; the equilibrium being restored through your body, which could not be restored through the glass.[12]If the tube be exhausted of air, a non electric lining in contact with the wire is not necessary; forin vacuo, the electrical fire will fly freely fromthe inner surface, without a non-electric conductor: but air resists its motion; for being itself an electricper se, it does not attract it, having already its quantity. So the air never draws off an electric atmosphere from any body, but in proportion to the non-electrics mix'd with it: it rather keeps such an atmosphere confin'd, which from the mutual repulsion of its particles, tends to dissipation, and would immediately dissipatein vacuo.—And thus the experiment of the feather inclosed in a glass vessel hermetically sealed, but moving on the approach of the rubbed tube, is explained: When an additional quantity of the electrical fluid is applied to the side of the vessel by the atmosphere of the tube, a quantity is repelled and driven out of the inner surface of that side into the vessel, and there affects the feather, returning again into its pores, when the tube with its atmosphere is withdrawn; not that the particles of that atmosphere did themselves pass through the glass to the feather.——And every other appearance I have yet seen, in which glass and electricity are concern'd, are, I think, explain'd with equal ease by the same hypothesis. Yet, perhaps, it may not be a true one, and I shall be obliged to him that affords me a better.
35. Thus I take the difference between non electrics and glass, an electricper se, to consist in these two particulars. 1st, That a non-electric easily suffers a change in the quantity of the electrical fluid it contains. Youmay lessen its whole quantity by drawing out a part, which the whole body will again resume; but of glass you can only lessen the quantity contain'd in one of its surfaces; and not that, but by supplying an equal quantity at the same time to the other surface; so that the whole glass may always have the same quantity in the two surfaces, their two different quantities being added together. And this can only be done in glass that is thin; beyond a certain thickness we have yet no power that can make this change. And, 2dly, that the electrical fire freely removes from place to place, in and through the substance of a non-electric, but not so through the substance of glass. If you offer a quantity to one end of a long rod of metal, it receives it, and when it enters, every particle that was before in the rod, pushes its neighbour quite to the further end, where the overplus is discharg'd; and this instantaneously where the rod is part of the circle in the experiment of the shock. But glass, from the smallness of its pores, or stronger attraction of what it contains, refuses to admit so free a motion; a glass rod will not conduct a shock, nor will the thinnest glass suffer any particle entring one of its surfaces to pass thro' to the other.
36. Hence we see the impossibility of success, in the experiments propos'd, to draw out the effluvial virtues of a non-electric, as cinnamon for instance, and mixing them with the electrical fluid, to convey them with that intothe body, by including it in the globe, and then applying friction, etc. For though the effluvia of cinnamon, and the electrical fluid should mix within the globe, they would never come out together through the pores of the glass, and so go to the prime conductor; for the electrical fluid itself cannot come through; and the prime conductor is always supply'd from the cushion, and that from the floor. And besides, when the globe is filled with cinnamon, or other non-electric, no electrical fluid can be obtain'd from its outer surface, for the reason before-mentioned. I have try'd another way, which I thought more likely to obtain a mixture of the electrical and other effluvia together, if such a mixture had been possible. I placed a glass plate under my cushion, to cut off the communication between the cushion and floor; then brought a small chain from the cushion into a glass of oil of turpentine, and carried another chain from the oil of turpentine to the floor, taking care that the chain from the cushion to the glass touch'd no part of the frame of the machine. Another chain was fix'd to the prime conductor, and held in the hand of a person to be electrised. The ends of the two chains in the glass were near an inch distant from each other, the oil of turpentine between. Now the globe being turn'd, could draw no fire from the floor through the machine, the communication that way being cut off by the thick glass plate under the cushion: it must then draw it through thechains whose ends were dipt in the oil of turpentine. And as the oil of turpentine being an electricper se, would not conduct what came up from the floor, was obliged to jump from the end of one chain, to the end of the other, through the substance of that oil, which we could see in large sparks; and so it had a fair opportunity of seizing some of the finest particles of the oil in its passage, and carrying them off with it: but no such effect followed, nor could I perceive the least difference in the smell of the electrical effluvia thus collected, from what it has when collected otherwise; nor does it otherwise affect the body of a person electrised. I likewise put into a phial, instead of water, a strong purgative liquid, and then charged the phial, and took repeated shocks from it, in which case every particle of the electrical fluid must, before it went through my body, have first gone through the liquid when the phial is charging, and returned through it when discharging, yet no other effect followed than if it had been charged with water. I have also smelt the electrical fire when drawn through gold, silver, copper, lead, iron, wood, and the human body, and could perceive no difference; the odour is always the same where the spark does not burn what it strikes; and therefore I imagine it does not take that smell from any quality of the bodies it passes through. And indeed, as that smell so readily leaves the electrical matter, and adheres to the knuckle receiving the sparks, and to otherthings; I suspect that it never was connected with it, but arises instantaneously from something in the air acted upon by it. For if it was fine enough to come with the electrical fluid through the body of one person, why should it stop on the skin of another?
But I shall never have done, if I tell you all my conjectures, thoughts, and imaginations, on the nature and operations of this electrical fluid, and relate the variety of little experiments we have try'd. I have already made this paper too long, for which I must crave pardon, not having now time to make it shorter. I shall only add, that as it has been observed here that spirits will fire by the electrical spark in the summer time, without heating them, whenFahrenheit's thermometer is above 70; so, when colder, if the operator puts a small flat bottle of spirits in his bosom, or a close pocket, with the spoon, some little time before he uses them, the heat of his body will communicate warmth more than sufficient for the purpose.
ADDITIONAL EXPERIMENT,proving that theLeyden Bottlehas no more electrical Fire in it when charged, than before; nor less when discharged: That in discharging, the Fire does not issue from the Wire and the Coating at the same Time, as some have thought, but that the Coating always receives what is discharged by the Wire, or an equal Quantity; the outer Surface being always in a negative State of Electricity, when the inner Surface is in a positive State.
ADDITIONAL EXPERIMENT,proving that theLeyden Bottlehas no more electrical Fire in it when charged, than before; nor less when discharged: That in discharging, the Fire does not issue from the Wire and the Coating at the same Time, as some have thought, but that the Coating always receives what is discharged by the Wire, or an equal Quantity; the outer Surface being always in a negative State of Electricity, when the inner Surface is in a positive State.
Place a thick plate of glass under the rubbing cushion, to cut off the communication of electrical fire from the floor to the cushion; then, if there be no fine points or hairy threads sticking out from the cushion, or from the parts of the machine opposite to the cushion, (of which you must be careful) you can get but a few sparks from the prime conductor, which are all the cushion will part with.
Hang a phial then on the prime conductor, and it will not charge, tho' you hold it by the coating.——But
Form a communication by a chain from the coating to the cushion, and the phial will charge.
For the globe then draws the electrical fire out of the outside surface of the phial, and forces it, through the prime conductor and wire of the phial, into the inside surface.
Thus the bottle is charged with its own fire, no other being to be had while the glass plate is under the cushion.
Hang two cork balls by flaxen threads to the prime conductor; then touch the coating of the bottle, and they will be electrified and recede from each other.
For just as much fire as you give the coating, so much is discharged through the wire upon the prime conductor, whence the cork balls receive an electrical atmosphere. But
Take a wire bent in the form of a C, with a stick of wax fixed to the outside of the curve, to hold it by; and apply one end of this wire to the coating, and the other at the same time to the prime conductor, the phial will be discharged; and if the balls are not electrified before the discharge, neither will they appear to be so after the discharge, for they will not repel each other.
Now if the fire discharged from the inside surface of the bottle through its wire, remained on the prime conductor, the balls would be electrified and recede from each other.
If the phial really exploded at both ends, and discharged fire from both coating and wire, the balls would bemoreelectrified and recedefarther: for none of the fire can escape, the wax handle preventing.
But if the fire, with which the inside surface is surcharged, be so much precisely as is wanted by the outside surface, it will pass round through the wire fixed to the waxhandle, restore the equilibrium in the glass, and make no alteration in the state of the prime conductor.
Accordingly we find, that if the prime conductor be electrified, and the cork balls in a state of repellency before the bottle is charged, they continue so afterwards. If not, they are not electrified by that discharge.
Page 2, Sect. 1. We since find, that the fire in the bottle is not contained in the non-electric, butin the glass. All that is after said of thetopandbottomof the bottle, is true of theinsideandoutsidesurfaces, and should have been so expressed.See Sect.16,p. 16.
Page 6, Line 13. The equilibrium will soon be restoredbut silently, etc. This must have been a mistake. When the bottle is full charged, the crooked wire cannot well be brought to touch the top and bottom so quick, but that there will be a loud spark; unless the points be sharp, without loops.
Ibid. line ult.Outside: add, such moisture continuing up to the cork or wire.
Page 12, line 14.By candle-lightetc. From some observations since made, I am inclined to think, that it is not the light, but the smoke or non-electric effluvia fromthe candle, coal, and red-hot iron, that carry off the electrical fire, being first attracted and then repelled.
Page 13, line 15.Windmil wheels, &c. We afterwards discovered, that the afflux or efflux of the electrical fire, was not the cause of the motions of those wheels, but various circumstances of attraction and repulsion.
Page 16, line 21.LetAandBstand on wax, &c. We soon found that it was only necessary for one of them to stand on wax.
Page 19. in the title r.on.
Page 24, line 12. r. contact, line 24. confined.
Page 25, line 10. forstandr.hand.
Page 28, line 2.The consequence might perhaps be fatal, &c. We have found it fatal to small animals, but 'tis not strong enough to kill large ones. The biggest we have killed is a hen.
Page 31, line 20.Ringing of chimes, &c. This is since done.
Page 33, line 22.Fails after ten or twelve experiments.This was by a small bottle. And since found to fail after with a large glass.
Page 40, sect. 50, 51.Spirits must be heated before we can fire them, &c. We have since fired spirits without heating, when the weather is warm.
FINIS.
BOOKSPrinted and Sold byEdward Cave, at St.John's Gate.
I. Geography Reform'd: Or, A new System of General Geography according to an accurate Analysis of the Science, augmented with several necessary Branches omitted by former Authors. In four Parts.
1. Of the Nature and Principles of Geography; its ancient and present State in all Nations, its Usefulness to Persons of all Professions, and the Method of studying it; with its Analysis or Division into Species, according to former Authors, and a new Plan, shewing the Errors and Defects of those by Varenius, Sanson, la Mattiniere, Pere Castel, etc.
2. Of Mathematical Geography and its Branches, Astronomical and Geometrical: Shewing the several Divisions of the Earth by Regions, Hemispheres, Zones, Climates, Meridians and Parallels, etc.
3. Historical Geography and its Species, Natural; Civil; Ecclesiastical; National; Periodical, ancient, middle, modern; Parallel and Critical.
4. Of Technical Geography and its Branches; Representatory, by Globes and Maps; Synoptical, by Tables; and Explanatory, by Systems and Dictionaries.
Under each Branch is given an Account of its Object and Use, an Explanation of the Terms, the History of its Rise and Progress, with Rules for exhibiting it to the best Advantage. The whole illustrated with Notes and References to the principal Geographers whose different Sentiments are cited and examined. Designed for the Use of the Curious in general, and Students in particular. There is added a copious Index of the Terms contained in the Work, answering the End of a Dictionary of General Geography. The Second Edition. Price 3s. 6d. bound.
II. Memoirs of the Royal Academy of Surgery at Paris.
Containing Remarks, with practical Observations, on Tumours of the Gall Bladder, on the Thigh, and the Trachea Arteria; on the Use of the Trepan; of Wounds in the Brain, Exfoliation of the Cranium, Cases of pregnant Women, faulty Anus in new born Children, Abscesses in the Fundament, Stones encysted in the Bladder, Obstructions to the Ejaculation of the Semen, an inverted Eyelid, extraneous Bodies retained in the Oesophagus,discharged through Abscesses; of Bronchotomy, Gastrotomy, native Hare-lips; of the Cæsarean Operation; a new Method of extracting the Stone from the Bladder, on a Cancer of the Breast, an elastic Truss for Hernias, remarkable Hernias of the Stomach, and through the Foramen Ovale. Of a pulmonary Abscess, &c. Translated from the Original, dedicated to the French King. In two Volumes, Octavo. Price 8s.
III. A Treatise of Comets, containing, 1. An Explication of all the various Appearances of the late Comet, both in its own Trajectory and the Firmament of fixt Stars, to its setting in the Sun Beams: Illustrated with a Plan of the Earth's and Comet's Orbits. 2. The History of Comets from the earliest Account of those kinds of Planets to the present Time; wherein the Sentiments of the Ancient and Modern Philosophers are occasionally displayed. With Remarks on the Intentional End of Comets, and the Nature and Design of Saturn's Ring. The Distance, Velocity, Size, Solidity, and other Properties of those Bodies considered; and the wonderful Phænomena of their Tails and Atmospheres accounted for. Illustrated also by a Copper-Plate. By G. Smith. Price 1s.
IV. The Natural History of Mount Vesuvius, with the Explanation of the various Phenomena that usually attend the Eruptions of this celebrated Volcano. Translated from the original Italian, composed by the Royal Academy of Sciences at Naples, by Order of the King of the Two Sicilies. Price 2s. stitch'd, or 2s. 6d. bound.
[1]We suppose every particle of sand, moisture, or smoke, being first attracted and then repelled, carries off with it a portion of the electrical fire; but that the same still subsists in those particles, till they communicate it to something else; and that it is never really destroyed.—So when water is thrown on common fire, we do not imagine the element is thereby destroyed or annihilated, but only dispersed, each particle of water carrying off in vapour its portion of the fire, which it had attracted and attached to itself.
We suppose every particle of sand, moisture, or smoke, being first attracted and then repelled, carries off with it a portion of the electrical fire; but that the same still subsists in those particles, till they communicate it to something else; and that it is never really destroyed.—So when water is thrown on common fire, we do not imagine the element is thereby destroyed or annihilated, but only dispersed, each particle of water carrying off in vapour its portion of the fire, which it had attracted and attached to itself.
[2]Our tubes are made here of green glass, 27 or 30 inches long, as big as can be grasped. Electricity is so much in vogue, that above one hundred of them have been sold within these four months past.
Our tubes are made here of green glass, 27 or 30 inches long, as big as can be grasped. Electricity is so much in vogue, that above one hundred of them have been sold within these four months past.
[3]To charge a bottle commodiously through the coating, place it on a glass stand; form a communication from the prime conductor to the coating, and another from the hook to the wall or floor. When it is charged, remove the latter communication before you take hold of the bottle, otherwise great part of the fire will escape by it.
To charge a bottle commodiously through the coating, place it on a glass stand; form a communication from the prime conductor to the coating, and another from the hook to the wall or floor. When it is charged, remove the latter communication before you take hold of the bottle, otherwise great part of the fire will escape by it.
[4]The river that washes one side ofPhiladelphia, as theDelawaredoes the other; both are ornamented with the summer habitations, of the citizens, and the agreeable mansions of the principal people of this colony.
The river that washes one side ofPhiladelphia, as theDelawaredoes the other; both are ornamented with the summer habitations, of the citizens, and the agreeable mansions of the principal people of this colony.
[5]An electrified bumper, is a small thin glass tumbler, near filled with wine, and electrified as the bottle. This when brought to the lips gives a shock, if the party be close shaved, and does not breathe on the liquor.
An electrified bumper, is a small thin glass tumbler, near filled with wine, and electrified as the bottle. This when brought to the lips gives a shock, if the party be close shaved, and does not breathe on the liquor.
[6]Thunder-gusts are sudden storms of thunder and lightning, which are frequently of short duration, but sometimes produce mischievous effects.
Thunder-gusts are sudden storms of thunder and lightning, which are frequently of short duration, but sometimes produce mischievous effects.
[7]See the ingenious essays on electricity in the Transactions, by Mr Ellicot.
See the ingenious essays on electricity in the Transactions, by Mr Ellicot.
[8]See the first sixteen Sections of my former Paper, calledFarther Experiments, &c.
See the first sixteen Sections of my former Paper, calledFarther Experiments, &c.
[9]See § 10 ofFarther Experiments, &c.
See § 10 ofFarther Experiments, &c.
[10]In the dark the electrical fluid may be seen on the cushion in two semi-circles or half-moons, one on the fore part, the other on the back part of the cushion, just where the globe and cushion separate. In the fore crescent the fire is passing out of the cushion into the glass; in the other it is leaving the glass, and returning into the back part of the cushion. When the prime conductor is apply'd to take it off the glass, the back crescent disappears.
In the dark the electrical fluid may be seen on the cushion in two semi-circles or half-moons, one on the fore part, the other on the back part of the cushion, just where the globe and cushion separate. In the fore crescent the fire is passing out of the cushion into the glass; in the other it is leaving the glass, and returning into the back part of the cushion. When the prime conductor is apply'd to take it off the glass, the back crescent disappears.
[11]Gilt paper, with the gilt face next the glass, does well.
Gilt paper, with the gilt face next the glass, does well.
[12]See farther experiments, § 15.
See farther experiments, § 15.