Imágenes de página
PDF
ePub

I do not remember any experiment by sun's surface, with a swiftness so prodigious! which it appeared that high rectified spirit Must not the smallest particle conceivable will not conduct; perhaps you have made have, with such a motion, a force exceeding such. This I know, that wax, rosin, brim- that of a twenty-four pounder, discharged stone, and even glass, commonly reputed elec- from a cannon? Must not the sun diminish trics, per se will, when in a fluid state, con- exceedingly by such a waste of matter; and duct pretty well. Glass will do it when only the planets, instead of drawing nearer to red hot. So that my former position, that him, as some have feared, recede to greater only metals and waters were conductors, and distances through the lessened attraction. other bodies more or less such as they par- Yet these particles, with this amazing motook of metal or moisture, was too general. tion, will not drive before them, or remove, the least or lightest dust they meet with: and the sun, for aught we know, continues of his ancient dimensions, and his attendants move in their ancient orbits.

Your conception of the electric fluid, that it is incomparably more subtle than air, is undoubtedly just. It pervades dense matter with the greatest ease; but it does not seem to mix or incorporate willingly with mere air, as it does with other matter. It will not quit common matter to join with air. Air obstructs, in some degree, its motion. An electric atmosphere cannot be communicated at so great a distance, through intervening air, as through a vacuum. Who knows then, but there may be as the ancients thought, a region of this fire above our atmosphere, prevented by our air, and its own too great distance for attraction, from joining our earth? Perhaps where the atmosphere is rarest, this fluid may be densest, and nearer the earth where the atmosphere grows denser, this fluid may be rarer; yet some of it be low enough to attach itself to our highest clouds, and thence they becoming electrified, may be attracted by, and descend towards the earth, and discharge their watery contents, together with that ethereal fire. Perhaps the aurora boreales are currents of this fluid in its own region, above our atmosphere, becoming from their motion visible. There is no end to conjectures. As yet we are but novices in this branch of natural knowledge.

May not all the phenomena of light be more conveniently solved, by supposing universal space filled with a subtle elastic fluid, which, when at rest, is not visible, but whose vibrations affect that fine sense in the eye, as those of air do the grosser organs of the ear? We do not, in the case of sound, imagine that any sonorous particles are thrown off from a bell, for instance, and fly in strait lines to the ear; why must we believe that luminous particles leave the sun and proceed to the eye? Some diamonds, if rubbed, shine in the dark, without losing any part of their matter. I can make an electrical spark as big as the flame of a candle, much brighter, and, therefore, visible further; yet this is without fuel; and I am persuaded, no part of the electric fluid flies off in such case to distant places, but all goes directly, and is to be found in the place to which I destine it. May not different degrees of the vibration of the above mentioned universal medium, occasion the appearance of different colours? I think the electric fluid is always the same; yet I find that weaker and stronger sparks differ in apparent colour, some white, blue, purple, red; the strongest, white; weak ones, red. Thus different degrees of vibration given to the air produce the seven different sounds in music, analagous to the seven colours, yet the me

You mention several differences of salts in electrical experiments. Were they all equally dry? Salt is apt to acquire moisture from a moist air, and some sorts more than others. When perfectly dried by lying before a fire, or on a stove, none that I have tried will con-dium, air, is the same. duct any better than so much glass.

New flannel, if dry and warm, will draw the electric fluid from non-electrics, as well as that which has been worn.

I wish you had the convenience of trying the experiments you seem to have such expectations from, upon various kinds of spirits, salt, earth, &c. Frequently, in a variety of experiments, though we miss what we expected to find, yet something valuable turns out, something surprising, and instructing, though unthought of.

If the sun is not wasted by expenditure of light, I can easily conceive that he shall otherwise always retain the same quantity of matter; though we should suppose him made of sulphur constantly flaming. The action of fire only separates the particles of matter, it does not annihilate them. Water, by heat raised into vapour, returns to the earth in rain; and if we could collect all the particles of burning matter that go off in smoke, perhaps they might, with the ashes, weigh as much as the body before it was fired: and if we could

I thank you for communicating the illustra-put them into the same position with regard tion of the theorem concerning light. It is very curious. But I must own I am much in the dark about light. I am not satisfied with the doctrine that supposes particles of matter called light continually driven off from the

to each other, the mass would be the same as before, and might be burnt over again. The chymists have analysed sulphur, and find it composed, in certain proportions, of oil, salt, and earth; and having, by the analysis, disco

vered those proportions, they can, of those ingredients, make sulphur. So we have only to suppose, that the parts of the sun's sulphur, separated by fire, rise into his atmosphere, and there being freed from the immediate action of the fire, they collect into cloudy masses, and growing, by degrees, too heavy to be longer supported, they descend to the sun, and are burnt over again. Hence the spots appearing on his face, which are observed to diminish daily in size, their consuming edges being of particular brightness.

It is well we are not as poor Galileo was, subject to the inquisition for philosophical heresy. My whispers against the orthodox doctrine, in private letters, would be dangerous; but your writing and printing would be highly criminal. As it is, you must expect some censure, but one heretic will surely ex

cuse another.

cer.

I am heartily glad to hear more instances of the success of the poke-weed, in the cure of that horrible evil to the human body, a canYou will deserve highly of mankind for the communication. But I find in Boston they are at a loss to know the right plant, some asserting that it is what they call Mechoachan, others other things. In one of their late papers it is publicly requested that a perfect description may be given of the plant, its places of growth, &c. I have mislaid the paper, or would send it to you. I thought you had described it pretty fully.* B. FRANKLIN.

E. Kinnersley, at Boston, to Benjamin Franklin.

New Experiments.-Paradoxes inferred from them.-Difference in the Electricity of a Globe of Glass charged, and a Globe of Sulphur Difficulty of ascertaining which is positive and which negative.

February 3, 1752.

I HAVE the following experiments to communicate: I held in one hand a wire, which was fastened at the other end to the handle of a pump, in order to try whether the stroke from the prime conductor, through my arms, would be any greater than when conveyed

*As the poke-weed, though out of place, is introduced here, we shall translate and insert two extracts of letters from Dr. Franklin to M. Dubourg, the French translator of a small collection of his works, on the

same subject.

"LONDON, March 27, 1773.

“I apprehend that our poke-weed is what the botanists term phytolacca. This plant bears berries as large as peas: the skin is black, but it contains a crimson

juice. It is this juice, thickened by evaporation in the sun, which was employed. It caused great pain, but some persons were said to have been cured. I am not quite certain of the facts; all that I know is, that Dr. Colden had a good opinion of the remedy."

"LONDON, April 23, 1773. "You will see by the annexed paper by Dr. Solander, that this herb, poke-weed, in which has been found a specific remedy for cancers, is the most common species

of phytolacca. (Phytolacca decandria L.")

only to the surface of the earth, but could discover no difference.

I placed the needle of a compass on the point of a long pin, and holding it in the atmosphere of the prime conductor, at the distance of about three inches, found it to whirl round like the flyers of a jack, with great rapidity.

I suspended with silk a cork ball, about the bigness of a pea, and presented to it rubbed amber, sealing-wax, and sulphur, by each of which it was strongly repelled; then I tried rubbed glass and china, and found that each of these would attract it, until it became electrified again, and then it would be repelled as at first; and while thus repelled by the rubbed glass or china, either of the others when rubbed would attract it. Then I electrified the ball, with the wire of a charged phial, and presented to it rubbed glass (the stopper of a decanter) and a china tea-cup, by which it was as strongly repelled as by the wire; but when I presented either of the other rubbed electrics, it would be strongly attracted, and when I electrified it by either of these, till it became repelled, it would be attracted by the wire of the phial, but be repelled by its coating.

These experiments surprised me very much, and have induced me to infer the following parodoxes.

1. If a glass globe be placed at one end of a prime conductor and a sulphur one at the other end, both being equally in good order, and in equal motion, not a spark of fire can be obtained from the conductor; but one globe will draw out, as fast as the other gives in.

2. If a phial be suspended on the conductor, with a chain from its coating to the table, and only one of the globes be made use of at a time, 20 turns of the wheel for instance, will charge it; after which, so many turns of the other wheel will discharge it; and as many more will charge it again.

3. The globes being both in motion, each having a separate conductor, with a phial suspended on one of them, and the chain of it fastened to the other, the phial will become charged; one globe charging positively, the other negatively.

4. The phial being thus charged, hang it in like manner on the other conductor; set both wheels a going again, and the same number of turns that charged it before, will now discharge it; and the same number repeated, will charge it again.

5. When each globe communicates with the same prime conductor, having a chain hanging from it to the table, one of them, when in motion (but which I cannot say) will draw fire up through the cushion, and discharge it through the chain; the other will draw it up through the chain, and discharge it through the cushion.

I should be glad if you would send to my house for my sulphur globe, and the cushion belonging to it, and make the trial; but must caution you not to use chalk on the cushion, some fine powdered sulphur will do better. If, as I expect, you should find the globes to charge the prime conductor differently, I hope you will be able to discover some method of determining which it is that charges positively.-I am, &c. E. KINNERSLEY.

1

PHILADELPHIA, March 2, 1752.

From these experiments one may be certain that your 2d, 3d, and 4th proposed experiments, would succeed exactly as you suppose, though I have not tried them, wanting time. I imagine it is the glass globe that charges positively, and the sulphur negatively, for these reasons: 1. Though the sulphur globe seems to work equally well with the glass one, yet it can never occasion so large and distant a spark between my knuckle and the conductor, when the sulphur one is working, as when the glass one is used; which, I suppose, is occaB. Franklin to E. Kinnersley. sioned by this, that bodies of certain bigness Probable Course of the different Attractions and cannot so easily part with a quantity of elecRepulsions of the two electrified Globes mention-trical fluid they have and hold attracted withed in the two preceding Letters. in their substance, as they can receive an additional quantity upon their surface by way I THANK you for the experiments commu- of atmosphere. Therefore so much cannot be nicated. I sent immediately for your brim-drawn out of the conductor, as can be thrown stone globe, in order to make the trials you on it. 2. I observe that the stream or brush desired, but found it wanted centres, which I of fire, appearing at the end of a wire, conhave not time now to supply; but the first nected with the conductor, is long, large, and leisure I will get it fitted for use, try the ex- much diverging, when the glass globe is used, periments, and acquaint you with the result. and makes a snapping (or rattling) noise: In the mean time I suspect, that the differ- but when the sulphur one is used, it is short, ent attractions and repulsions you observed, small, and makes a hissing noise; and just proceeded rather from the greater or smaller the reverse of both happens, when you hold quantities of the fire you obtained from differ- the same wire in your hand, and the globes are ent bodies, than from its being of a different worked alternately: the brush is large, long, kind, or having a different direction. In diverging, and snapping (or rattling) when haste, B. FRANKLIN. the sulphur globe is turned; short, small, and hissing, when the glass globe is turned.When the brush is long, large, and much diverging, the body to which it joins seems to me to be throwing the fire out; and when the contrary appears, it seems to be drinking in. 3. I observe, that when I hold my knuckle before the sulphur globe, while turning, the stream of fire between my knuckle and the globe seems to spread on its surface, as if it flowed from the finger; on the glass globe it is otherwise. 4. The cool wind (or what was called so) that we used to feel as coming from an electrified point, is, I think, more sensible when the glass globe is used, than when the sulphur one. But these are hasty thoughts. As to your fifth paradox, it must likewise be true, if the globes are alternately worked; but if worked together, the fire will neither come up nor go down by the chain, because one globe will drink it as fast as the other produces it.

B. Franklin to E. Kinnersley. Reasons for supposing, that the glass Globe charges positively, and the Sulphur negatively. -Hint respecting a leather Globe for Experiments when travelling.

PHILADELPHIA, March 16, 1752.

SIR,-Having brought your brimstone globe to work, I tried one of the experiments you proposed, and was agreeably surprised to find, that the glass globe being at one end of the conductor, and the sulphur globe at the other end, both globes in motion, no spark could be obtained from the conductor, unless when one globe turned slower or was not in so good order as the other; and then the spark was only in proportion to the difference, so that turning equally, or turning that slowest which worked best, would again bring the conductor to afford no spark.

I should be glad to know, whether the effects would be contrary if the glass globe is solid, and the sulphur globe is hollow; but I have no means at present of trying.

I found also, that the wire of a phial charged by the glass globe, attracted a cork ball that had touched the wire of a phial charged by the brimstone globe, and vice versa, so that the cork continued to play between the two phials, In your journeys, your glass globes meet just as when one phial was charged through with accidents, and sulphur ones are heavy the wire, the other through the coating, by and inconvenient.Query. Would not a thin the glass globe alone. And two phials charg-plane of brimstone, cast on a board, serve on ed, the one by the brimstone globe, the other by the glass globe, would be both discharged by bringing their wires together, and shock the person holding the phials.

occasion as a cushion, while a globe of leather stuffed (properly mounted) might receive the fire from the sulphur, and charge the conductor positively! Such a globe would be

[ocr errors]

in no danger of breaking* I think I can conceive how it may be done; but have not time to add more than that I am, B. FRANKLIN.

The early LETTERS of Dr. Franklin on electricity having been translated into French, and printed at Paris; the Abbe Mazeas, in a letter to Dr. Stephen Hales, dated St. Germain, May 20, 1752, gives the following Account (printed in the Philosophical Transactions) of the Experiment made at Marly, in pursuance of that proposed by Dr. Franklin.

THE Philadelphian experiments, that Mr. Collinson, a member of the Royal Society, was so kind as to communicate to the public, having been universally admired in France, the king desired to see them performed. Wherefore the duke d'Ayen offered his majesty his country-house at St. Germain, where M. de Lor, professor of experimental philosophy, should put those of Philadelphia in execution. His majesty saw them with great satisfaction, and greatly applauded Messieurs Franklin and Collinson. These applauses of his majesty having excited in Messieurs de Buffon, d'Alibard, and de Lor, a desire of verifying the conjectures of Mr. Franklin, upon the analogy of thunder and electricity, they prepared themselves for making the experiment.

M. d'Alibard chose for this purpose a garden situated at Marly, where he placed upon an electrical body a pointed bar of iron, of forty feet high. On the 10th of May, twenty minutes past two in the afternoon, a stormy cloud having passed over the place where the bar stood, those that were appointed to observe it, drew near, and attracted from it sparks of fire, perceiving the same kind of commotions as in the common electrical riments.

expe

M. de Lor, sensible of the good success of this experiment, resolved to repeat it at his house in the Estrapade, at Paris. He raised a bar of iron ninety-nine feet high, placed upon a cake of rosin, two feet square, and three inches thick. On the 18th of May, between | four and five in the afternoon, a stormy cloud having passed over the bar, where it remained half an hour, he drew sparks from the bar, like those from the gun barrel, when in the electrical experiments, the globe is only rubbed by the cushion, and they produced the same noise, the same fire, and the same crackling. They drew the strongest sparks at the distance of nine lines, while the rain,

*The discoveries of the late ingenious Mr. Symmer, on the positive and negative electricity produced by the mutual friction of white and black silk, &c. afford hints for further improvements to be made with this view. VoL. II. . . . 2 . 24.

mingled with a little hail, fell from the cloud, without either thunder or lightning; this cloud being, according to all appearance, only the consequence of a storm, which happened elsewhere.-I am, with a profound respect, your most humble and obedient servant, G. MAZEAS.

A more particular Account of the Circumstances and Success of this extraordinary Experiment was laid before the Royal Academy of Sciences at Paris, three days afterwards, in a Memorial by M. d'Alibard, viz.

Extrait d'un Memoire de M. D'Alibard. Lu a l'Academie Royale des Sciences, le 13 Mai, 1752.

"EN suivant la route que M. Franklin nous a tracée, j'ai obtenu une satisfaction complette. Voici les préparatifs, le procédé et je succès.

six lieues de Paris au milieu d'une belle 1. J'ai fait faire à Marly-la-ville, située à plaine dont le sol est fort élevé, une verge de fer ronde, d'environ un pouce de diametre, longue de 40 pieds, et fort pointue par son extrémité supérieure; pour lui ménager une pointe plus fine, je l'ai fait armer d'acier trempé et ensuite brunir, au défaut de dorure, pour la préserver de la rouille; outre cela, cette verge de fer est courbée vers son extrémité inférieure en deux coudes à angles éloigné de deux pieds du bout inférieur, et le aigus quoiqu'arrondis; le premier coude est second est en sens contraire à trois pieds du premier.

"2. J'ai fait planter dans un jardin trois grosses perches de 28 à 29 pieds, disposées en triangle, et éloignées les unes des autres d'environ huit pieds; deux de ces perches sont contre un mur, et la troisieme est au-dedans du jardin. Pour les affermir toutes ensemble, l'on à cloué sur chacune des entretoises à vingt pieds de hauteur; et comme le grand vent agitoit encore cette espéce dé'difice, l'on a attaché au haut de chaque perche de longs cordages, qui tenant lieu d'aubans, répondent par le bas à de bons piquets fortement enfoncés en terre à plus de 20 pieds des perches.

"3. J'ai fait construire entre les deux perches voisines du mur, et adosser contre ce mur une petite guérite de bois capable de contenir un homme et une table.

"4. J'ait fait placer au milieu de la guérite une petite table d'environ un demi-pied de hauteur: et sur cette table j'ai fait dresser et affermir un tabouret electrique. Ce tabouret n'est autre chose qu'une petite planche quarrée, portée sur trois bouteilles à vin; il n'est fait de cette matiere que pour suppléer au defaut d'un gâteau de résine qui me manquoit.

"5. Tout étant ainsi préparé, j'ai fait elever | nuée d'orage et de grêle ne fut pas plus d'un perpendiculairement la verge de fer au milieu quart-d'heure à passer au zénith de notre mades trois perches, et je l'ai affermie en l'attach-chine, et l'on n'entendit que ce seul coup de ant à chacune des perches avec de forts cor- tonnerre. Sitôt que le nuage fut passé, et dons de soie par deux endroits seulement. qu'on ne tira plus d'étincelles de la verge de Les premiers liens sont au haut des perches, fer, M. le Prieur de Marly fit partir le sieur environ trois pouces au-dessous de leurs ex- Coiffier lui-même, pour m'apporter la lettre trémités, supérieures; les seconds vers la suivante, qu'il m'écrivit à la hâte. moitié de leur hauteur. Le bout inférieur de la verge de fer est solidement appuyé sur le milieu du tabouret electrique, où j'ai fait creuser un trou propre à le recevoir.

"6. Comme il étoit important de garantir de la pluie le tabouret et les cordons de soie, parce qu'ils laisseroient passer la matiéré électrique s'ils étoient mouillés, j'ai pris les précautions nécessaires pour en empécher. C'est dans cette vue que j'ai mis mon tabouret sous la guérite, et que j'avois fait courber ma verge de fer à angles aigus; afin que l'eau qui pourroit couler le long de cette verge, ne pût arriver jusques sur le tabouret. C'est aussi dans le même dessein que j'ai fait clouer sur le haut et au milieu de mes perches, à trois pouces au-dessus des cordons de soie, des especes de boîtes formées de trois petites planches d'environ 15 pouces de long, qui couvrent par-dessus et par les côtês une pareille longueur des cordons de soie, sans les toucher.

"Il s'agissoit de faire, dans le tems de l'orage, deux observations sur cette verge de fer ainsi disposée; l'une étoit de remarquer á sa pointe une aigrette lumineuse, semblable à celle que l'on apperçoit à la pointe d'une aiguille, quand on l'oppose assez prés d'un corps actuellement électrisé; l'autre étoit de tirer de la verge de fer des étincelles, comme on en tire du canon de fusil dans les expériences électriques; et afin de se garantir des piquûres de ces étincelles, j'avois attaché le tenon d'un fil d'archal au cordon d'une longue fiole pour lui server de manche..

"Le Mécredi 10 Mai, 1752, entre deux et trois heures après midi, le nommé Coiffier, ancien dragon, que j'avois chargé de faire les observations en mon absence, ayant entendu un coup de tonnerre assez fort, vole aussitôt à la machine, prend la fiole avec le fil d'archal, présente le tenon du fil à la verge, en voit sortir une petite étincelle brilliante, et en entend le pétillement; il tire une seconde étincelle plus forte que la premiere et avec plus de bruit! il appelle ses voisins, et envoie chercher M. le Prieur. Celuici accourt de toutes ses forces; les paroissiens voyant la précipitation de leur curé, s'imaginent que le pauvre Coiffier a éte tué du tonnerre; l'allarme se répand dans le village; la grêle qui survient n'empêche point le troupeau de suivre son pasteur. Cet honnête ecclésiastique arrive près de la machine, et voyant qu'il n'y avoit point de danger, met luimême la main à l'œuvere et tire de fortes étincelles. La

Je vous annonce, Monsieur, ce que vous attendez: l'expérience est complette. Aujourd'hui à deux heures 20 minutes après midi, le tonnerre a grondé directement sur Marly; le coup a été assez fort. L'envie de vous obliger, et la curiosité m'ont tiré de mon fauteuil, où j'étois occupé à lire: je suis allé chez Coiffier, qui déja m'avoit dépêché un enfant que j'ai rencontré en chemin, pour me prier de venir ; j'ai doublé le pas à travers un torrent de grêle. Arrivé à l'endroit où est placée la tringle coudée, j'ai présenté le fil d'archal, en avançant successivement vers la tringle, à un pouce et demi, ou environ; il est sorti de la tringle une petite colonne de fer bleuâtre sentant le soufre, qui venoít frapper avec une extrême vivacité le tenon du fil d'archal, et occasionnoit un bruit semblable à celui qu'on feroit en frappant sur la tringle avec une clef. J'ai répété l'expérience au moins six fois dans l'espace d'environ quatre minutes, en présence de plusieurs personnes, et chaque expérience que j'ai faite a dure l'espace d'un pater et d'un ave. J'ai voulu continuer ; l'action du feu s'est ralentie peu à peu; j'ai approché plus près, et n'ai plus tiré que quelques étincellss, et enfin rien n'a paru.

Le coup de tonnerre qui a occasionné cet évenement, n'a été suivi d'aucun autre; tout s'est terminé par une abondance de gréle. J'étois si occupé dans le moment de l'expérience de ce que voyois, qu'ayant été frappé au bras un peu au-dessus du coude, je ne puis dire si c'est en touchant au fil d'archal ou à la tringle: je ne me suis pas plaint du mal que m'avoit fait le coup dans le moment que je l'ai reçu; mais comme la douleur continuoit, de retour chez moi, j'ai découvert mon bras en présence de Coiffier, et nous avons apperçu une meurtrissure tournante autour du bras, samblable à celle que feroit un coup de fil d'archal, si j'en avois été frappé à nud. En revenant de chez Coiffier, j'ai recontré M. le Vicaire, M. de Milly, et le maitre d'école, à qui j'ai rapporté ce qui venoit d'arriver; ils se sont plaints tous les trois qu'ils sentoient une odeur de soufre qui les frappoit davantage à mesure qu'ils s'approchoient de moi: j'ai porté chez moi la même odeur, et mes domestiques s'en sont apperçus sans que je leur aye rien dit.

Voilà Monsieur, un récit fait à la héte, mais naif et vrai j'atteste, et vous pouvez assurer que je suis prêt à rendre témoignage

« AnteriorContinuar »