« ZurückWeiter »
by a succession of bubbles, till the spirit is above it. From the foot of this rod, a wire (the all dried away. Perhaps the observations on thickness of a goose-quill) came through a these little instruments may suggest and be covered glass tube in the roof, and down applied to some beneficial uses. It has been through the well of the staircase; the lower thought, that water reduced to vapour by end connected with the iron spear of a pump. heat was rarefied only fourteen thousand On the staircase opposite to my chamber times, and on this principle our engines for door, the wire was divided; the ends separatraising water by fire are said to be constructed about six inches, a little bell on each end; ed: but if the vapour so much rarefied from and between the bells a little brass ball suswater, is capable of being itself still farther pended by a silk thread, to play between and rarefied to a boundless degree by the applica-strike the bells when clouds passed with election of heat to the vessels or parts of vessols tricity in them. After having frequently containing the vapour (as at first it is applied drawn sparks and charged bottles from the to those containing the water) perhaps a much bell of the upper wire, I was one night greater power may be obtained, with little awaked by loud cracks on the staircase. additional expense. Possibly too, the power Starting up and opening the door, 1 perceivof easily moving water from one end to the ed that the brass ball instead of vibrating as other of a moveable beam (suspended in the usual between the bells, was repelled and middle like a scale-beam) by a small degree kept at a distance from both; while the fire of heat, may be applied advantageously to passed sometimes in very large quick cracks some other mechanical purposes.
from bell to bell; and sometimes in a contiB. FRANKLIN. nued dense white stream, seemingly as large
as my finger, whereby the whole staircase
was enlighted as with sunshine, so that one Experiments, Observations, and Facts, tend
might see to pick up a pin.* And from the ing to support the Opinion of the utility but conceive that a numbert of such conduc
apparent quantity thus discharged, I cannot of long pointed Rods, for securing Build- tors must considerably lessen that of any apings from Damage by Strokes of Light- proaching cloud, before it comes so near as to ning:-Read at the committee appointed deliver its contents in a general stroke:-an to consider the erection of conductors to effect not to be expected from bars unpoint
ecure the magazines at Purfleet, Aug. 27, ed ; if the above experiment with the blunt 1772.
end of the wire is deemed pertinent to the case.
EXPERIMENT II. The prime conductor of an electric machine, A, B (See the plate) being supported
The pointed wire under the prime conduce about 10 inches and a half above the table by tor continuing of the same height, pinch it a wax-stand, and under it erected a pointed between the thumb and finger near the top, wire 7 inches and a half high, and one fifth so as just to conceal the point; then turning of an inch thick, and tapering to a sharp the globe, the electrometer will rise and mark point, and communicating with the table; the full charge. Slip the fingers down so as when the point (being uppermost) is covered to discover about half an inch of the wire, by the end of a finger, the conductor may be then another half inch, and then another ; at full charged, and the electrometer, c, (Mr. every one of these motions discovering more Henley's) will rise to the height indicating a and more of the pointed wire; you will see full charge: but the moment the point is un- the electrometer fall quick and proportionably, covered, the ball of the electrometer drops, stopping, when you stop. If you slip down showing the prime conductor to be instantly the whole distance at once, the ball falls indischarged and nearly emptied of its electri- stantly down to the stem. city. Turn the wire its blunt end upwards
OBSERVATION. (which represents an unpointed bar) and no such effect follows, the electrometer remain
From this experiment it seems that a ing at its usual height when the prime con
greater effect in drawing off the lightning ductor is charged.
* Mr. de Romas saw still greater quantities of light. ning brought down by the wire of his kite. He had
explosions from it, the noise of which greatly resem.
blent that of thunder, and were heard (from without) What quantity of lightning, a high pointed into the heart of the city, notwithstanding the various rod well communicating with the earth may had the shape of a spindle eight inches long and five be expected to discharge from the clouds si
lines in diameter. Yer from the time of explosion to lently in a short time, is yet unknown; but I the end of the experiment, no lightning was seen above, have reason from a particular fact to think it if fire issuing from it were observed 10 be an inch may at some times be very great. In Phila- thick and ten feet long." --Sec Dr. Priestley's History delphia I had such a rod fixed to the top of of Electricity, pages 131–138. first edition.
| Twelve were proposed on and near the magazines my chimney, and extending about nine feet at Purfleet.
from the clouds may be expected from long conductor therefore shows, that a quantity of puinted rods, than from short ones; I mean its atmosphere was drawn from the end where from such as show the greatest length, above the electrometer is placed to the part immethe building they are fixed on.
diately over the large body, and there accu
mulated ready to strike into it with its whole EXPERIMENT III.
undiminished force, as soon as within the Instead of pinching the point between the striking distance; and, were the prime conthumb and finger, as in the last experiment, ductor moveable like a cloud, it would apkeep the thumb and finger each at near an proach the body by attraction till within that inch distance from it, but at the same height, distance. The swift motion of clouds, as the point between them. In this situation, driven by the winds, probably prevents this though the point is fairly exposed to the prime happening so often as otherwise it might do: conductor, it has little or no effect; the elec- for, though parts of the cloud may stoop totrometer rises to the height of a full charge. wards a building as they pass, in consequence But the moment the fingers are taken away, of such attraction, yet they are carried forthe ball falls quick to the stem.
ward beyond the striking distance, before they
could by their descending come within it. To explain this, it is supposed, that one reason of the sudden effect produced by a Attach a small light lock of cotton to the long naked pointed wire is, that (by the re- underside of the prime conductor, so that it pulsive power of the positive charge in the may hang down towards the pointed wire prime conductor) the natural quantity of elec- mentioned in the first experiment. Cover the iricity contained in the pointed wire is driven point with your finger, and the globe being down into the earth, and the point of the wire turned, the cotton will extend itself, stretchmule strongly negative; whence it attracts ing down towards the finger, as at a; but on the electricity of the prime conductor more uncovering the point, it instantly flies up to strongly thar. bodies in their natural state the prime conductor, as at b, and continues would do; the small quantity of common there as long as the point is uncovered. The matter in the point, not being able by its al- moment you cover it again, the cotton flies tractive force to retain its natural quantity down again, extending itself towards the of the electric fluid, against the force of that finger; and the same happens in degree, if repulsion.-But the finger and thumb being (instead of the finger) you use, uncovered, the • substantial and blunt bodies, though as near blunt end of the wire uppermost. the prime conductor, hold up better their own natural quantity against the force of that repulsion; and so, continuing nearly in their To explain this, it is supposed that the cotnatural state, they jointly operate on the elec- ton, by its connexion with the prime conduct-. tric fluid in the point, opposing its descent and or, receives from it a quantity of its electriaiding the point to retain it; contrary to the city; which occasions its being attracted by repelling power of the prime conductor, which the finger that remains still in nearly its nawould drive it down.–And this may also serve tural state. But when a point is opposed to to explain the different powers of the point in the cotton, its electricity is thereby taken the preceding experiment, on the slipping from it, faster than it căn at a distance be down the finger and thumb to different dis- supplied with a fresh quantity from the contances.
ductor. Therefore being reduced nearer to Hence is collected, that a pointed rod erect- the natural state, it is attracted up to the ed between two tall chimnies, and very little electrified prime conductor; rather than higher (an instance of which I have seen) can-down, as before, to the finger. not have so good an effect, as if it had been Supposing farther that the prime conductor erected on one of the chimnies, its whole represents a cloud charged with the electric length above it.
fluid ; the cotton, a ragged fragment of cloud
(of which the underside of great thunderIf, instead of a long pointed wire, a large chimney or highest part of a building. We
clouds are seen to have many) the finger, a solid body (to represent a building without a then may conceive that when such a cloud point) be brought under and as near the prime conductor, when charged; the ball of the passes over a building, some one of its ragged electrometer will fall a little; and on taking by the chimney of other high part of the edi
under-hanging fragments may be drawn down away- the large body, will rise again.
fice; creating thereby a more easy commu
nication between it and the great cloud.—But Its rising again shows that the prime con- a long pointed rod being presented to this ductor lost little or none of its electric charge, fragment, may occasion its receding, like the as it had done through the point: the falling cotton, up to the great cloud; and thereby' of the ball while the large body was under the increase, instead of lessening the distance, su
Vol. II. ...28
as often to make it greater than the striking every help to obtain, even from broken partial distance. Turning the blunt end of a wire metalline conductors. uppermost (which represents the unpointed It has also been suggested, that from such bar) it appears that the same good effect is electric experiments nothing certain can be not from that to be expected. A long pointed concluded as
, to the great operations of narod, it is therefore imagined, may prevent some ture ; since it is often seen, that experiments strukes; as well as conduct others that fall which have succeeded in small, in large have upon it, when a great body of cloud comes on failed. It is true that in mechanics this has so heavily that the above repelling operation sometimes happened. But when it is consion fragments cannot take place.
dered that we owe our first knowledge of the
nature and operations of lightning, to observaEXPERIMENT VI.
tions on such small experiments; and that on Opposite the side of the prime conductor, carefully comparing the most accurate acplace separately isolated by wax stems, Mr. counts of former facts, and the exactest relaCanton's two boxes with pith balls suspended tions of those that have occurred since, the by fine linen threads. On each box, lay a effects have surprisingly agreed with the theowire six inches long and one fifth of an inch ry ; it is humbly conceived that in natura) thick, tapering to a sharp point; but so laid philosophy, in this branch of it at least, the as that four inches of the pointed end of one suggestion has not so much weight; and that
ire, and an equal length of the blunt end of the farther new experiments now adduced in the other, may project beyond the ends of the recommendation of long sharp-pointed rods, boxes; and both at eighteen inches distance may have some claim to credit and considerafrom the prime conductor. Then charging tion. the prime conductor by a turn or two of the It has been urged too, that though points globe, the balls of each pair will separate ; may have considerable effects on a small prime those of the box, whence the point projects conductor at small distances; yet on great most, considerably; the others less. Touch clouds and at great distances, nothing is to be the prime conductor, and those of the box with expected from them. To this it is answered, the blunt point will collapse, and join. Those that in those small experiments it is evident connected with the point will at the same the points act at a greater than the striking time approach cach other, till within about an distance; and in the large way, their service inch, and there remain.
is only expected where there is such nearness of the cloud, as to endanger a stroke ; and
there, it cannot be doubted the points must This seems a proof, that though the small have some effect. And if the quantity dissharpened part of the wire must have had a charged by a single pointed rod may be so less natural quantity in it, before the opera- considerable as I have shown it; the quantity tion, than the thick blunt part ; yet a greater discharged by a number will be proportionally quantity was driven down from it to the balls. greater. 'Thence it is again inferred, that the pointed But this part of the theory does not depend rod is ren lered more negative : and farther, alone on small experiments. Since the practhat if a stroke must fall from the cloud over tice of erecting pointed rods in America (now a building, furnished with such a rod, it is near twenty years) five of them have been more likely to be drawn to that pointed rod, struck by lightning, viz. Mr. Raven's and than to a blunt ope; as being more strongly Mr. Maine's, in South Carolina ;. Mr. Tucknegative, and of course its attraction stronger. er's, in Virginia ; Mr. West's and Mr. MoulAnd it seems more eligible, that the lightning der’s, in Philadelphia. Possibly there may should fall on the point of the conductor (pro- have been more that have not come to my vided to convey it into the earth) than on any knowledge. But in every one of these, the other part of the building, thence to proceed lightning did not fall upon the body of the to such conductor: which end is also more house, but precisely on the several points of likely to be obtained by the length and lofti- the rods; and, though the conductors were ness of the rod; as protecting more exten- sometimes not sufficiently large and comsively the building under it.
plete, was conveyed into the earth, without It has been objected, that erecting pointed any material damage to the buildings. l'acts rods upon edifices, is to invite and draw the then in great, as far as we have them aulightning into them; and therefore dangerous. thenticated, justify the opinion that is drawn Were such rods to be erected on buildings, from the experiments in small as above without continuing the communication quite related. down into the moist earth, this objection might It has also been objected, that unless we then have weight; but when such complete knew the quantity that might possibly be disconductors are made, the lightning is invited charged at one stroke from the clouds, we not into the building, but into the earth, the cannot be sure we have provided sufficient situation it aims at, and which it always seizesconductors; and therefore cannot depend on
their conveying away all that may fall on power in the clouds of collecting it; yet an their points. Indeed we have nothing to form accumulation and force beyond what mankind a judgment by in this but past facts; and we has hitherto been acquainted with is scarce to know of no instance where a complete con- be expected. *
B. F. ductor to the moist earth has been insuffi- August 27, 1772. cient, it half an inch diameter. It is probable that
many strokes of lightning have been conveyed through the common leaden pipes af
To Professor Landriani, Italy. fixed to horses to carry down the water from On the Utility of Electrical Conductors. the roof to the ground: and there is no ac
PHILADELPHIA, Oct. 14, 1787. count of such pipes being melted and destroyed, as must sometimes have happened if they the Utility of Electrical Conductors, which
I HAVE received the excellent work upon had been insufficient. We can then only judge of the dimensions proper for a conductor with great pleasure, and beg you to accept my
you had the goodness to send me. I read it of lightning, as we do of those proper for a sincere thanks for it. conductor of rain, by past observation. And as we think a pipe of three inches bore suf- the number of conductors much increased,
Upon my return to this country, I found ficient to carry off the rain that falls on a square of 20 feet, because we never saw such many proofs of their efficacy in preserving a pipe glutted by any shower; so we may their utility. Among other instances, my
buildings from lightning having demonstrated judge a conductor of an inch diameter, more ilman sufficient for any stroke of lightning that which occasioned the neighbours to run in to
own house was one day attacked by lightning, will fall on its point. It is true, that if another deluge should happen wherein the win- But no damage was done, and my family was
give assistance, in case of its being on fire. dows of heaven are to be opened, such pipes only found a good deal frightened with the viomay be unequal to the falling quantity; and lence of the explosion. if God for our sins should think tit to rain fire
Last year, my house being enlarged, the upon us, as upon solne cities of old, it is not conductor was obliged to be taken down.. expected that our conductors of whatever found, upon examination, that the pointed size, should secure our houses against a mi-termination of copper, which, was originally racle. Probably as water drawn up into the nine inches long, and about one third of an air and there forining clouds, is disposed to inch in diameter in its thickest part, had fall again in rain by its natural gravity, as heen almost entirely melted; and that its soon as a number of particles sufficient to wake a drop can get together; so when the connexion with the rod of iron below was clouds are (by whatever means) over or un- this invention has proved of use to the au
very slight. Thus, in the course of time, dercharged with the electric fluid, to a degree thor of it, and has added this personal adsufficient to attract them towards the earth, the equilibrium is restored, before the differ- vantage to the pleasure he before received,
from having been useful to others.. ence becomes great beyond that degree.
Mr. Rittenhouse, our astronomer, has inMr. Lane's electrometer, for limiting precise- formed me, that having observed with his ly the quantity of a shock that is to be administered in a medical view, may serve to within the field of his view, he has remark
excellent telescope, many conductors that are inake this more easily intelligible. The dis
ed in various instances, that the points were charging knob does by a screw approach the melted in like manner. There is no example conluctor to the distance intended, but there of a house, provided with a perfect conductreinains fixed. Whatever power there may be in the glass globe to collect the fulminat
* The immediate occasion of the dispute concerning ing fluid, and whatever capacity of receiving the preference between pointed and biunt conductors and accumulating it there may be in the bottle of lightning, arose as follows:-A powder mill having or glass jar; yet neither the accumulation with lightning, the English board of ordinance applied por the discharge ever exceeds the destined to their painter, Mr. Wilson, then of some note as an quantity. Thus, were the clouds always at
their magazines at Purtleet. Mr. Wilsen having ad. a certain fixed distance from the earth, all vised a blunt conductor, and it being understood that discharges would be made when the quantity Dr. Franklin's opinion formed upon the spot was for a accumulated was equal to the distance: but Royal Society, and by them as usual, to a committee, there is a circumstance which by occasionally who, after consultation, prescribed a method conform. lessening the distance, lessens the discharge; lightning, having under particular circumstances, fallen to wit, the moveableness of the clouds, and upon one of the buildings and its apparatus in May their being drawn nearer to the earth by at-1727; the subject came again into violent agitation, traction when electrified; so that discharges again referred to a new committee, which committee are thereby rendered more frequent and of confirmed the decision of the first committee; it procourse less violent. Hence whatever the duced an acrimonious controversy in the Royal Society,
and a series of pamphlcts; which, however ended in quantity may be in nature, and whatever the I the triumple of the Franklinian theory.
clectrician, for a method to prevent the like accident to
or, which has suffered any considerable da- | been accompanied with proper medicine and mage; and even those which are without regimen, under the direction of a skilful phythem have suffered little, since conductors sician. It may be, too, that a few great strokes, have become common in this city.
as given in my method, may not be so proper B. FRANKLIN. as many small ones; since by the account
from Scotland of a case, in which two hun
dred shocks from a phial were given daily, it John Pringle, M. D.
seems, that a perfect cure has been made. As On the Effects of Electricity in Paralytic Cases. to any uncommon strength supposed to be in
CRAVEN-STREET, Dec. 21, 1757. the machine used in that case, I imagine it In compliance with your request, I send could have no share in the effect produced; you the following account of what I can at since the strength of the shock from charged present recollect relating to the effects of elec- glass, is in proportion to the quantity of surtricity in paralytic cases, which have fallen face of the glass coated : so that my shock under my observation.
from those large jars, must have been much Some years since, when the newspapers greater than any that could be received from made mention of great cures performed in Ita- a phial held in the hand. ly and Germany, by means of electricity, a
B. FRANKLIN. number of paralytics were brought to me from different parts of Pennsylvania, and the neigh
Electrical Experiments on Amber. bouring provinces, to be electrised, which I
Saturday, July 3, 1702. did for them at their request. My method To try, at the request of a friend, whether was, to place the patient first in a chair, on amber finely powdered might be melted and an electric stool, and draw a number of large run together again by means of the electric strong sparks from all parts of the affected fluid, I took a piece of small glass tube, about limb or side. Then I fully charged two six- | two inches and a half long, the bore about one gallon glass jars, each of which had about twelfth of an inch diameter, the glass itself three square feet of surface coated; and sent about the same thickness; I introduced into this the united shock of these through the affect- tube some powder of amber, and with two ed linb or limbs, repeating the stroke com- pieces of wire nearly fitting the bore, one inmonly three times each day. The first thing serted at one end, the other at the other, I observed, was an immediate greater sensible rammed the powder hard between them in warmth in the lame limbs that had received the middle of the tube, where it stuck fast, the stroke, than in the others; and the next and was in length about half an inch. Then morning the patients usually related, that leaving the wires in the tube, I made them they had in the night felt a pricking sensa- part of the electric circuit, and discharged tion in the flesh of the paralytic limbs; and through them three rows of my case of botwould sometimes show a number of small tles. The event was, that the glass was red spots, which they supposed were occasion-broke into very small pieces, and those dised by those prickings. The limbs, too, were persed with violence in all directions. As I found more capable of voluntary motion, and did not expect this, I had not, as in other exseemed to receive strength. A man, for in- periments, laid thick paper over the glass to stance, who could not the first day lift the lame save my eyes, so several of the pieces struck hand from off his knee, would the next day my face smartly, and one of them cut my lip raise it four or five inches, the third day higher; a little so as to make it bleed. I could find and on the fifth day was able, but with a fee- no part of the amber; but the table where ble languid motion, to take off his hat. These the tube lay was stained very black in spots, appearances gave great spirits to the patients, such as might be made by a thick smoke and made them hope a perfect cure ; but I do forced on it by a blast, and the air was filled not remember that I ever saw any amendment with a strong smell, somewhat like that from after the fifth day; which the patients per- burnt gunpowder. Whence I imagined, that ceiving, and finding the shocks pretty severe, the amber was burnt, and had exploded as they became discouraged, went home, and in gunpowder would have done in the same cira short time relapsed; so that I never knew cumstances. any advantage from electricity in palsies that That I might better see the effect on the was permanent. And how far the apparent | amber, I made the next experiment in a tube temporary advantage might arise from the ex- formed of a card-rolled up and bound strongly ercise in the patients' journey, and coming with packthread. Its bore was about one daily to my house, or from the spirits given eighth of an inch diameter. I rammed powby the hope of success, enabling them to ex- der of amber into this as I had done in the ert more strength in moving their limbs, I other, and as the quantity of amber was will not pretend to say.
greater, I increased the quantity of electric Perhaps some permanent advantage might Auid by discharging through it at once five have been obtained, if the electric shocks had rows of my bottles. On opening the tube, I