Abbildungen der Seite

found that some of the powder had exploded, at about the distance of three or four inches an impression was made on the tube, though from that part which is most distant from the it was not hurt, and most of the powder re- balls, and you will see the balls separate from maining was turned black, which I suppose each other, being positively electrified by the might be by the smoke forced through it from natural portion of electricity, which was in the burned part: some of it was hard; but as the box, and which is driven to the further part it powdered again when pressed by the fingers, of it by the repulsive power of the atmosphere I suppose that hardness not to arise from melt- in the excited glass. * Touch the box near the ing any parts in it, but merely from my ram- little balls (the excited glass continuing in the ming the powder when I charged the tube. same state) and the balls will again unite;

B. FRANKLIN. the quantity of electricity which had been

driven to this part being drawn off by your

finger. Withdraw then both your finger and To Thomas Ronayne, Esq. Cork, Ireland. the glass at the same instant, and the quantity On the Electricity of the Fogs in Ireland.

of electricity which remained in the box,

uniformly diffusing itself, the balls will again LONDON, April 20. 1766.

be separated; being now in a negative state. I have received your very obliging and very While things are in this situation, begin once ingenious letter by captain Kearney. Your more to excite your glass, and hold it above observations upon the electricity of fogs, and the box, but not too near, and you will find, the air in Ireland, and upon different circum- that when brought within a certain distance, stances of storms, appear to me very curious, the balls will at first approach each other, beand I thank you for them. There is not, in ing then in a natural state. In proportion my opinion, any part of the earth whatever, as the glass is brought nearer, they will which is, or can be, naturally in a state of ne- again separate, being positive. When the gative electricity: and though different cir- glass is moved beyond them, and at some litcumstances may occasion an inequality in the tle further distance, they will unite again, bedistribution of the fluid, the equilibrium is im- ing in a natural state. When it is entirely mediately restored by means of its extreme removed, they will separate again, being then subtlety, and of the excellent conductors with made negative. The excited glass in this which the humid earth is amply provided. I experiment may represent a cloud positively am of opinion, however, that when a cloud, charg which you see is capable of producwell charged positively, passes near the earth, ing in this manner all the different changes it repels and forces down into the earth, that in the apparatus, without the least necessity natural portion of electricity, which exists for supposing any negative cloud. near its surface, and in buildings, trees, &c. I am nevertheless fully convinced, that so as actually to reduce them to a negative there are negative clouds; because they somestate before it strikes them. I am of opinion times absorb, through the medium of the aptoo, that the negative state in which you have paratus, the positive electricity of a large jar, frequently found the balls, which are suspend the hundredth part of which the apparatus ed from your apparatus, is not always occa- itself would have not been able to receive or sioned by clouds in a negative state; but contain at once. In fact, it is not difficult to more commonly by clouds positively electri- conceive, that a large cloud, highly charged fied, which have passed over them, and which positively, may smaller clouds to a in their passage have repelled and driven off a negative state, when it passes above or near part of the electrical matter, which naturally them, by forcing a part of their natural porexisted in the apparatus; so that what remain-tion of the fluid either to their inferior sured after the passing of the clouds, diffusing faces, whence it may strike into the earth, or itself uniformly through the apparatus, the to the opposite side, whence it may strike inwhole became reduced to a negative state. to the adjacent clouds; so that when the large

If you have read my experiments made in cloud has passed off to a distance, the small continuation of those of Mr. Canton, you will clouds shall remain in a negative state, exreadily understand this; but you may easily actly like the apparatus; the former (like the make a few experiments, which will clearly latter) being frequently insulated bodies, haydemonstrate it. Let a common glass be warm-ing communication neither with the earth nor ed before the fire that it may continue very with other clouds. Upon the same principle dry for some time; set it upon a table, and it may easily be conceived, in what manner place upon it the small box made use of by a large negative cloud may render others poMr. Canton, so that the balls may hang a lit- sitive. tle beyond the edge of the table. Rub ano- The experiment which you mention, of ther glass, which has previously been warm- filling your glass, is analogous to one which ed in a similar manner, with a piece of black I made in 1751 or 1752. I had supposed in silk or silk handkerchief, in order to electrify my preceding letters, that the pores of glass it. Hold then the glass above the little box, I were smaller in the interior parts than near

the surface, and that on this account they plate touches the upper part of the fish, with a prevented the passage of the electrical fluid. metal rod : then observe, if the force of the To prove whether this was actually the case shock be the same as to all the persons formor not, I ground one of my phials in a part ing the circle, or is stronger than before. where it was extremely thin, grinding it con- Repeat this experiment with this differsiderably beyond the middle, and very near ence: let two or three of the persons forming to the opposite superfices, as I found, upon the circle, instead of holding by the hand, breaking it after the experiment. It was hold each an uncharged electrical bottle, so charged nevertheless after being ground, that the little balls at the end of the wires equally well as before, which convinced me, may touch, and observe, after the shock, if that my hypothesis on this subject was erro- these wires will attract and repel light bodies, neous. It is difficult to conceive where the and if a ball of cork, suspended by a long silk immense superfluous quantity of electricity on string between the wires, a little distance from the charged side of a glass is deposited. the bottles, will be alternately attracted and

I send you my paper concerning meteors, repelled by them.
which was lately published here in the Phi-
losophical Transactions, immediately after a
paper by Mr. Hamilton on the same subject.

TO M. Dubourg,
B. FRANKLIN. On the Analogy between Magnetism and Elec-


LONDON, March 10, 1773. Mode of ascertaining, whether the Power, giving a Shock to those who touch either

As to the magnetism, which seems prothe Surinam Eel, or the Torpedo, be elec- duced by electricity, my real opinion is, that

these two powers of nature have no affinity trical.

with each other, and that the apparent pro1. Touch the fish with a stick of dry seal- duction of magnetism is purely accidental. ing-wax, or a glass rod, and observe if the The matter may be explained thus: shock be communicated by means of those 1st, The earth is a great magnet. bodies.

2dly, There is a subtle fluid, called the Touch the same fish with an iron, or other magnetic fluid, which exists in all ferrugimetalline rod.

nous bodies, cqually attracted by all their parts, If the shock be communicated by the latter and equally diffuseu through their whole subbody, and not by the others, it is probably not stance; at least where the equilibrium is not the mechanical effect, as has been supposed, of disturbed by a power superior to the attracsome muscular action in the fish, but of a sub- tion of the iron. tle fluid, in this respect analogous at least to

3dly, This natural quantity of the magnetic the electric fluid.

fluid, which is contained in a given piece of 2. Observe farther, whether the shock can iron, may be put in motion so as to be more be conveyed without the metal being actually rarefied in one part and more condensed in in contact with the fish, and if it can, whe- another; but it cannot be withdrawn by any ther, in the space between, any light appear, force that we are yet made acquainted with, and a slight noise or crackling be heard.

so as to leave the whole in a negative state, If so, these also are properties common to at least relatively to its natural quantity; the electric fluid.

neither can it be introduced so as to put the 3. Lastly, touch the fish with the wire of iron into a positive state, or 'render it plus. a small Leyden bottle, and if the shock can be in this respect, therefore, magnetism difers received across, observe whether the wire will from electricity. attract and repel light bodies, and you feel a 4thly, A piece of soft iron allows the mag. shock, while holding the bottle in one hand, netic fluid which it contains to be put in moand touching the wire with the other.

tion by a moderate force, so that being placed If so, the Auid, capable of producing such in a line with the magnetic pole of the earth, effects, seems to have all the known properties it immediately acquires the properties of a of the electric fluid.

magnet; its magnetic fluid being drawn or

forced from one extremity to the other; and Addition, 12th of August, 1772,

this effect continues as long as it remains in In consequence of the Experiments and Disco- the same position, one of its extremities beveries 'made in France by Mr. Walsh, and coming positively magnetised, and the other communicated by him to Dr. Franklin.

negatively. This temporary magnetism Let several persons, standing on the floor, ceases as soon as the iron is turned east and hold hands, and let one of them touch the fish, west, the fluid immediately diffusing itself so as to receive a shock. If the shock be felt equally through the whole iron, as in its naby all, place the fish flat on a plate of metal, tural state. and let one of the persons holding hands touch 5thly, The magnetic fluid in hard iron, or his plate, while the person farthest from the steel, is put in motion with more difficulty, requiring a force greater than the earth to given portion of steel into a magnet of a force excite it; and when once it has been forced proportioned to its capacity of retaining its from one extremity of the steel to the other, magnetic fluid in the new position in which it it is not easy for it to return; and thus a bar is placed, without letting it return. Now this. of steel is converted into a permanent magnet. power is different in different kinds of steci,

6thly, A great heat, by expanding the sub- but limited in all kinds whatever. stance of this steel, and increasing the dis

B. FRANKLIN. tance between its particles, affords a passage to the electric fluid, which is thus again restored to its proper equilibrium; the bar ap- To Messrs. Dubourg and d’Alibard.* pearing no longer to possess magnetic virtue. Concerning the Vode of rende: ing Aleat tender 7thly, A bar of steel which is not magnetic,

by Electricity being placed in the same position, relatively to the pole of the earth, which the magnetic the mode of rendering meat tender by electri

My answer to your questions concerning needle assumes, and in this position being city, can only be founded upon conjecture ; heated and suddenly cooled, becomes a perma- for I have not experiments enough to warrant nent magnet. The reason is, that while the the facts. All that I can say at present is, bar was hot, the magnetic fluid which it na- that I think electricity might be employed for turally contained was easily forced from one this purpose, and I shall state what follows as extremity to the other by the magnetic virtue the observations or reasons, which make me of the earth; and that the hardness and condensation, produced by the sudden cooling of presume so.

It has been observed, that lightning, by the bar, retained it in this state without per- rarefying and reducing into vapour the moistmitting it to resume its original situation.

ure contained in solid wood, in an oak, for inSthly, The violent vibrations of the parti- stance, has forcibly separated its filures, and cles of a steel bar, when forcibly struck in the broken it into small splinters; that by penesame position, separate the particles in such trating intimately the hardest metals

, as iron, a manner during their vibration, that they it has separated the parts in an instant, so as permit a portion of the magnetic fluid to pass, to convert a perfect solid into a state of fluidinfluenced by the natural magnetism of the earth; and it is afterwards so forcibly retain- ity: it is not then improbable, that the same

subtle matter, passing through the bodies of ed by the re-approach of the particles when animals with rapidity, should possess sufficient the vibration ceases, that the bar becomes a

force to produce an effect nearly similar. permanent magnet.

The flesh of animals, fresh killed in the 9thly, An electric shock passing through a usual manner, is firm, hard, and not in a very needle in a like position, and dilating it for eatable state, because the particles adhere too an instant, renders it, for the same reason, a

forcibly to each other. At a certain period, permanent magnet; that is, not by imparting the cohesion is weakened and in its progress magnetism to it, but by allowing its proper towards putrefaction, which tends to produce magnetic fluid to put itself in motion. lothly, Thus, there is not in reality more call tender, or is in that state most proper to

a total separation, the flesh becomes what we magnetism in a given piece of steel after it is be used as our food. become magnetic, than existed in it before.

It has frequently been remarked, that aniThe natural quantity is only displaced or re

nals killed by lightning putrefy inmediately. pelled. Hence it follows, that a strong ap: This cannot be invariably the case, since a paratus of magnets may charge millions of bars of steel, without communicating to them not be sufficient to tear and divide the fibres

quantity of lightning sufficient to kill, may any part of its proper magnetism; only put. and particles of flesh, and reduce them to that ting in motion the magnetism which already tender state, which is the prelude to putrefacexisted in these bars.

tion. Hence it is, that some animals killed I am chiefly indebted to that excellent phi- in this manner will keep longer than others. losopher of Petersburgh, Mr. Æpinus, for this But the putrefaction sometimes proceeds with hypothesis, which appears to me equally in- surprising celerity. A respectable person asgenious and solid. I I say, chiefly, because, as

sured me, that he once knew a remarkable it is many years since I read his book, which instance of this : a whole flock of sheep in I have left in America, it may happen, that 1 Scotland, being closely assembled under a tree, may have added to or altered it in some respect; and if I have misrepresented any thing, being rather late in the evening, the proprie

were killed by a flash of lightning; and it the error ought to be charged to my account, tor, desirous of saving something, sent per

If this hypothesis appears admissible, it will sons early the next morning to flay them: but serve as an answer to the greater part of your the putrefaction was such, and the stench so questions. I have only one remark to add, which is, that however great the force is of

* This letter has no date, but the one to which it is magnetism employed, you can only convert a an answer is dated May 1, 1773.

abominable, that they had not the courage to

To M. Dubourg, execute their orders, and the bodies were accordingly buried in their skins. It is not un- In Answer to some Queries concerning the reasonable to presume, that between the pe

choice of Glass for the Leyden esperiment. riod of their death and that of their putrefac


June 1, 1773. tion, a time intervened in which the flesh Sir,—I wish, with you, that some chemist might be only tender, and only sufficiently so (who should, if possible, be at the same time to be served at table. Add to this, that per- an electrician) would, in pursuance of the exsons, who have eaten of fowls killed by our cellent hints contained in your letter, underfeeble imitation of lightning (electricity) and take to work upon glass with the view you dressed immediately, have asserted, that the have recommended. By means of a perfect flesh was remarkably tender.

knowledge of this substance, with respect to The little utility of this practice has per- its electrical qualities, we might proceed with haps prevented its being much adopted. For more certainty, as well in making our own though it sometimes happens, that a company experiments, as in repeating those which unexpectedly arriving at a country-house, or have been made by others in different counan unusual conflux of travellers to an inn, tries, which I believe have frequently been may render it necessary, to kill a number of attended with different success on account of animals for immediate use; yet as travellers differences in the glass employed, thence ochave commonly a good appetite, little atten- casioning frequent inisunderstandings and contion has been paid to the trilling inconveni-trariety of opinions. ence of having their meat a little tough. As There is another circumstancen h to be. this kind of death is nevertheless more sud- desired with respect to glass, and that is, that den, and consequently less severe, than any it should not be subject to break when highly other, if this should operate as a motive with charged in the Leyden experiment. I have compassionate persons to employ it for ani- known eight jars broken out of twenty, and mals sacrificed for their use, they may con- at another time, twelve out of thirty-five. A duct the process thus:

similar loss would greatly discourage elecHaving prepared a battery of six large tricians desirous of accumulating a great glass jars (each from 20 to 4 pints) as for power for certain experiments. We have the Leyden experiment, and having establish- never been able hitherto to account for the ed a communication, as usual, from the inte-cause of such misfortunes. The first idea rior surface of each with the prime conduct which occurs is, that the positive electricity, or, and having given them a full charge being accumulated on one side of the glass, (which with a good machine may be executed rushes violently through it, in order to supin a few minutes, and may be estimated by ply the deficiency on the other side, and to rean electrometer) a chain which communicates store the equilibrium. This however, I cannot with the exterior of the jars must be wrapped conceive to be the true reason, when I conround the thighs of the fowl; after which sider, that a great number of jars being the operator, holding it by the wings, turned united, so as to be charged and discharged at back and made to touch behind, must raise it the same time, the breaking of a single jar so high that the head may receive the first will discharge the whole ; for, if the accident shock from the prime conductor. The ani- proceeded from the weakness of the glass, it mal dies instantly. Let the head be imme- is not probable, that eight of them should be diately cut off to make it bleed, when it may precisely of the same degree of weakness, as be plucked and dressed immediately. This to break every one at the same instant, it bequantity of electricity is supposed sufficient ing more likely that the weakest should for a turkey of ten pounds' weight, and per- break first, and, by breaking, secure the rest ; haps for a lamb. Experience alone will in- and again, when it is necessary to produce a form us of the requisite proportions for ani- certain effect, by means of the whole charge mals of different forms and ages. Probably passing through a determined circle (as, for not less will be required to render a small instance, to melt a small wire) if the charge, bird, which is very old, tender, than for a instead of passing in this circle, rushed through larger one, which is young. It is easy to fur- the sides of the jars, the intended effect nish the requisite quantity of electricity, by would not be produced; which, however, is employing a greater or less number of jars. contrary to fact. For these reasons, I susAs six jars, however, discharged at once, are pect, that there is, in the substance of the capable of giving a very violent shock, the glass, either some little globules of air, or operator must be very circumspect, lest he some portions of unvitrified sand or salt, into should happen to make the experiment on which a quantity of the electric fluid may

be his own flesh, instead of that of the fowl. forced during the charge, and there retained

B. FRANKLIN. till the general discharge: and that the force

being suddenly withdrawn, the elasticity of supported by them; for in the vacancies there the Auid acts upon the glass in which it is is nothing they can rest on. enclosed, not being able to escape hastily Air and water mutually attract each other. without breaking the glass. I offer this only Hence water will dissolve in air, as salt in as a conjecture, which I leave to others to water. examine.

The specific gravity of matter is not alterThe globe which I had that could not be ed by dividing the matter, though the superexcited, though it was from the same glass-fices be increased. Sixteen leaden bullets, house which furnished the other excellent of an ounce each, weigh as much in water as globes in my possession, was not of the same one of a pound, whose superfices is less. frit. The glass which was usually manu- Therefore the supporting of salt in water factured there, was rather of the green kind, is not owing to its superfices being increased. and chiefly intended for drinking-glasses and A lump of salt, though laid at rest at the bottles; but the proprietors being desirous of bottom of a vessel of water, will dissolve attempting a trial of white glass, the globe therein, and its parts move every way, till in question was of this frit. The glass not equally diffused in the water, therefore there being of a perfect white, the proprietors is a mutual attraction between water and salt. were dissatisfied with it, and abandoned their Every particle of water assumes as many of project. I suspected that too great a quantity salt as can adhere to it; when more is adof salt was admitted into the composition ; but ded, it precipitates, and will not remain susI am no judge of these matters.

pended. B. FRANKLIN. Water, in the same manner, will dissolve

in air, every particle di air assuming one or more particles of water. When too much is ad

ded, it precipitates in rain. Miss Stephenson.

But there not. being the same contiguity Concerning the Leyden Bottle. between the particles of air as of water, the

solution of water in air is not carried on LONDON, March 22, 1762. I must retract the charge of idleness in fresh accession of dry particles.

without a motion of the air, so as to cause a your studies, when I find you have gone through the doubly difficult task of reading so solves, will communicate to other parts that

Part of a fluid, having more of what it disbig a book, on an abstruse subject, and in a have less. Thus very salt water, coming in foreign language.

In answer to your question concerning the contact with fresh, communicates its saltness Leyden phial. — The hand that holds the bottle till all is equal, and the sooner if there is a little

motion of the water. receives and conducts away the electric fluid that is driven out of the outside by the repul- A stroke of a horse's hoof on the ground, in

Even earth will dissolve, or mix with air. sive power of that which is forced into the in- a bot dusty road, will raise a cloud of dust, side of the bottle. As long as that power re- that shall, if there be a light breeze, expand mains in the same situation, it must prevent the return of what it had expelled; though every way, till perhaps near as big as a comthe hand would readily supply the quantity if

mon house. It is not by mechanical motion it could be received. B. FRANKLIN.

communicated to the particles of dust by the hoof, that they fly so far, not by the wind, that they spread so wide; but the air near

the ground, more heated by the hot dust struck Physical and Meteorological Observations,

into it, is rarefied and rises, and in rising Conjectures, and Suppositions.—Read at

mixes with the cooler air, and communicates the Royal Society, June 3, 1756.

of its dust to it, and it is at length so diffused

as to become invisible. Quantities of dust The particles of air are kept at a distance are thus carried up in dry seasons: showers from each other by their mutual repulsion. wash it from the air, and bring it down again.

Every three particles, mutually and equal. For water attracting it stronger, it quits the ly repelling each other, must form an equilate- air, and adheres to the water. ral triangle.

Air, suffering continual changes in the deAll the particles of air gravitate towards grees of its heat, from various causes and cirthe earth, which gravitation compresses them, cumstances, and consequently, changes in its and shortens the sides of the triangles, specific gravity, must therefore be in contiotherwise their mutual repellency would nual motion. force them to greater distances from each A small quantity of fire mixed with water other.

(or degree of heat therein) so weakens the Whatever particles of other matter (not en- cohesion of its particles, that those on the surdued with that repellency) are supported in face easily quit it, and adhere to the particles air, must adhere to the particles of air, and be of air. Vol. II. ...2 T


« ZurückWeiter »