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balls will now touch one another, the threads it first touch some conducting substance; and, hanging perpendicularly, and parallel to each if the tube be managed dexterously, you may other. But if the cylinder of the machine be drive the feather through the room at pleasure. turned, by turning the winch, then the pith balls This experiment may be varied as follows: A will repel one another, more or less according as person may hold in his hand an excited tube of the electricity is more or less powerful. If the smooth glass, and another may hold an excited electrometer be hung to a prime conductor ne- rough glass tube, a stick of sealing-wax, or any gatively electrified, i.e. connected with the insu- other electric negatively electrified, at about one lated rubber of the machine, the balls will also re foot and a half distance from the smooth glass pel each other. If, in this state of repulsion, the tube ; a feather now may be let go between these prime conductor is touched with some conduct- two differently excited electrics, and it will leap ing substance not insulated, the pith balls will alternately from one electric to the other. immediately come together. But if, instead of (5.) Place a leaf of gold, silver, or other the conducting substance, the prime conductor metal, on the palm of the hand, and bring it is touched with an electric, as a stick of sealing within a few inches of an electrified conductor; wax, a piece of glass, &c., then the pith balls will it will be attracted and continue to move, altercontinue to repel each other; because the elec- nately from the hand to the conductor, as long tric fluid cannot be conducted through that as the latter is electrified, electric.
(6.) Suspend from the conductor, by a brass (2.) Take a small downy feather or a pith ballchain, a circular plate of copper, reaching to suspended by a thread, and, holding the thread, within an inch and a half or two inches of bring the ball near an electrified conductor, either the table. Directly under this plate place anopositive or negative: the ball will be attracted by ther of the same form, and a little larger, on the the electrified conductor, and adhere to it, until table. Turn the machine, and the fluid will pass its electricity is destroyed.
from the upper to the lower plate. If now small Such bodies as are positively electrified, tend to figures cut out of pasteboard, or pith of elder, diffuse their superabundant fluid amongst sur be introduced between the plates, they will rounding substances; and those that are negative, dance about with apparent vivacity, and someendeavour to acquire electric fluid: hence, times appear to course round the edge of the either state of electricity will produce attraction; lower plate. This experiment is represented by for if light bodies are to be moved, it is indiffe- fig. 4. rent whether the electrified surface attracts their (7.) The electrical bells furnish a pleasing natural electric fluid, or the matter to which it illustration of the attraction and repulsion of the is attached; for the attraction arises only from electric matter. They are variously constructed, the different proportions of these in any two but the form exhibited fig. 5 is the simplest. bodies, and will of course continue whilst that dif- The two outer bells are suspended by brass ference exists.
chains ; the middle bell and the two clappers (3.) Repeat the preceding experiment with a by fine silk threads. When the bells are attached ball or feather supported by a silk thread : the to the conductor, and the machine is turned very light body will first be attracted to the electrified gently, the fluid will pass along the chains to conductor, and will then recede froin it; nor can the two outer bells, but will not pass along the it again be brought in contact until it has touched silk to the clappers and middle bell. Thus the some conducting substance. Mr. Singer thus outer bells being charged with an extra quantity explains the cause of this :— The light body is of fluid will attract the clappers, but the moment here attracted for the same reason as before, but they touch the bells they become charged, and it is insulated, and consequently receives, by are repelled with such force as to cause them to contact with the electrified surface, a similar strike against the middle bell, on which they deelectric state; it therefore recedes from that sur- posit their electricity, and are again attracted. face, being attracted by the ambient air, or other By this means a constant ringing is kept up surrounding bodies; for they have their natural while the machine is turned. From the inside portion of electricity, and therefore differ from of the middle bell a brass chain passes to the the light body, which has either more or less; table, for the purpose of conveying away the fluid but the electrified surface does not differ from deposited on it by the clappers. A more elethe light body, and consequently cannot attract gant form of the electrical bells is thus made :it, till, by touching some conductor, its natural Fix eight bells near the edge of a circular board electric state is restored.
supported on four feet, fig. 6, having a glass (4.) The following is a very pleasing variety pillar e, in the centre, terminated by a point. oi the last-mentioned experiment -Take a glass On this point place the pointed wires used in tube, whether smooth or rough is not material, the last experiment, hanging from one of them, and, after having rubbed it, let a small light as d, a small glass clapper by a silken thread; feather be let out of your fingers at the distance and connecting the apparatus by a chain h, proof about eight or nine inches from it. This fea- ceeding from the prime conductor. On setting ther will be immediately attracted by the tube, the machine in motion, the wire will move round, and will stick very close to its surface for about and the clapper ring the bells. two or three seconds, and sometimes longer; (8.) Place a pointed wire on the machine, elecafter which it will be repelled ; and, if the tube trify the inside of a dry glass tumbler by holding be kept under it, the feather will continue float- it over the wire whilst the machine is in motion; ing in the air at a considerable distance from place some pith balls on the table and cover the tube, without coming near it again, except them with the electrified glass ; they will be
alternately attracted by it and the table, and con the prime conductor, and replace it in its marked tinue their motion for some time. See fig. 7. An place. The spider will now begin to move from instrument is constructed on purpose for this knob to knob, and continue this motion for a experiment, by which the dancing of the balls considerable time, sometimes for several hours, inay be kept up for any length of time, as it may The inside of the jar being charged positively, be connected with the conductor.
the spider is attracted by the knob A, which (9.) Insulate a circular ring of brass so as to communicates to it a small quantity of elecstand about an inch and a half from the flat sur- tricity; the spider then becoming possessed of face of a table; connect the brass ring with the same electricity with the knob A, is repelled the conductor of the electrical machine, and by it, and runs to the knob E, where it displace within it on the table, a very light and charges its electricity, and is then attracted by round glass ball of two inches diameter; the ball the knob A, and so on. Thus the jar is gradwill be attracted by the ring, touch it, and be- ually discharged; and, when the discharge is come electrified at the point of contact; this nearly completed, the spider finishes its motion. point will then recede and be attracted by the table, whilst another part of the ball is attracted
EFFECT OF POINTS ON THE ELECTRIC FLUID. by the ring; and, by the repetition of this pro 97. The facility with which pointed bodies cess, the ball is made to revolve and travel round transmit electricity has given rise to several the circumference of the ring.
very delicate and beautiful experiments on the (10.) Fasten a small piece of sealing-wax on the electrical apparatus, of which the following are End of a wire, and set fire to it. Then put the the most deserving of attention electrical machine in motion, and present the (1.) The Electrical Flies. These flies are comwax, just blown out, at the distance of a few poser of sınall brass wires, fig. 9, fixed into a inches from the prime conductor. A number of cap of brass, easily moveable upon an axis of the very fine filaments will immediately dart from the same metal, and exactly balanced, so that they Sealing-wax to the conductor, on which they may turn with the smallest force. The ends, will be condensed into a kind of net-work, re which ought to be very sharp, are all bent one sembling wool.
way, with regard to one another, as those beIf the wire with the sealing-wax be fixed into longing to a, b, in the figure ; though the two one of the roles of the conductor, and a piece of sets of points, constituting the two flies there paper be presented at a moderate distance to the represented, are contrary to each other; so that wax, just after it has been ignited, on putting the the whole flies must have a contrary motion. Trachine in motion, a net-work of wax will be Fixing the axle with the two flies upon the prime formed on the paper.
conductor, and working the machine, both will If the paper on which the way is thus re- begin to turn very swiftly, each in a direction ceived be gently warmed, by holding the back contrary to that of the points. In this manner, of it near the fire, the wax will adhere to it, with a powerful machine, several flies may be and thus the result of the experiment will be made to turn either in the same or in contrary direndered permanent. A remarkably fine ex- rections ; and by their gradual increase or deperiment of the same kind may be made with crease in size may represent a cone or other camphor. Let a silver spoon containing a piece figure ; for the course of each will be marked of lighted camphor be made to communicate by a line of fire, and thus the whole will exhibit with an electrified body, as the prime conductor a beautiful appearance in the dark. The light of a machine; while the conductor continues is more brilliant when the ends are slightly coelectrified, by keeping the machine in motion, vered with sealing-wax, grease, or other electric the camphor will throw out numerous ramifi- matter. The flies, in this experiment, turn the tations, and appear to shoot like a vegetable. same way whether the electricity be positive or
(11.) Take about a dozen of flaxen threads and negative; the reason of which is that in positive tie them together at top and bottom; annex electricity the fluid issues from the body electrithem to the conductor of the electrical machine; fied, and that in negative electricity it enters into when electrified the threads will separate from it. In the former case, the recoil of the fluid, each other, and the knot at the bottom rising which acts equally on the air and on the point they will assume a spheroidal figure, which from whence it issues, must continually urge will continue as long as they are electrified. the point the contrary way; and in negative
(12.) The following experiment we give as electricity, when the point solicits a continual being one of the earliest made by Dr. Franklin draught of electric matter from the air, the direct in illustration of the principle of attraction and impulse of the former must also produce a repulsion. Fig. 8 represents an electric jar, motion in the point in the course in which the having a wire C D E fastened on its outside, Auid itself moves. In vacuo no motion is prowhich is bent so as to have its knob E as high duced; because there is no air on which the as the knob A. A is a spider made of cork, fluid may act when it issues from the point. with a few short threads run through it to (2.) The Electrical Orrery, fig. 10, is another represent its legs. It is fastened at the end of instrument frequently used for showing the a silk thread, proceeding from the ceiling of the effect of points in the transmission of the elecmnom, or from any other support, so that it may tric fluid. The principle of its action is this: bang mid-way between the two knobs A and E, the ball S represents the sun, E the earth, and When the jar is not charged. Let the place of M the moon, connected by wires ac and bd; b the jar upon the table be marked; then is the centre of gravity between the earth and the jar, by bringing its knob A in contact with These three balls and their connecting
wires are hung and supported on the sharp point The action of the machine will cause the hairs of a wire A, which is stuck upright in the prime on the head to diverge from each other, and to conductor B of the electrical machine ; the earth stand on end. and moon hanging upon the sharp point of the 98. Such, says Mr, Singer, are the principal wire cae, in which wire is a pointed short pin, phenomena of inotion produced by the action of sticking out horizontally at c; and there is just electricity; they are susceptible of almost unsuch another pin at d, sticking out in the same limited variety, but uniformly result from the manner, in the wire that connects the earth and simples already stated, namely, the attraction the moon.
of the electric fluid for common matter, its When the cylinder of the electrical machine tendency to equal diffusion; and the occasional is turned, these balls and wires are electrified; interruption of these properties by non-conand the electrical fire, flying off horizontally ducting power and altered force of attraction. from the points c and d, causes S and E to move
LUMINOUS EXHIBITION OF ELECTRICITY. round their common centre of gravity a, and E and M to move round their common centre of
99. It may be necessary to observe here that gravity b. And as E and M are light, when all experiments made for the purpose of discompared with S and E, there is much less fric- playing the brilliancy of the electric matter, in rion on the point b, than S and E make about passing from one conducting substance to another, the point a. The weights of the balls may be should be made in a darkened room, as the preadjusted so, that E and M may go twelve times sence of either natural or artificial light robs round b, in the time that S and E go once them of more than half of their beauty. Th round a.
articles of apparatus, too, must be all free from (3.) The Electrical Inclined Plane affords dust, and perfectly dry, besides being a little another and a still more beautiful illustration of warm, otherwise the effect expected will not rethe same thing, showing also that a stream of sult; we think it particularly necessary to obthe electric matter issuing from points pos serve that in any experiment requiring the exsesses force sufficient to counteract the power of haustion of glass vessels the above precautions gravitation in light bodies. Fig. 11 represents are peculiarly needful, as we have seen some of the inclined plane, where A is a board of ma the following experiments utterly fail in the hogany, fourteen inches long and four inches hands of public lecturers merely from inattention broad; BBBB are four glass pillars, three to them. tenths of an inch in thickness; the length of the 100. To render the electrical fluid luminous two longer is seven inches, and that of the two it must be collected in considerable quantities, shorter is five inches.
and the brilliancy of the display will depend on From the longer to the shorter pillars are the particular configuration of the conducting stretched two fine brass wires, parallel to each surface over which it is made to pass. The other, and tightened by screws which pass light evolved in ordinary cases, says Mr. Singer, through the brass balls which surmount the pil- extends only to faint flashes and scintillations, lars. On these wires the axis of the fly C rests, sparks being only produced when these effects the ends of which are formed like a small pulley, are concentrated, as they are in the electrical having a groove in them to prevent their slip- machine by the action of its conductors. ping off the wires, and to guide the fly when in 101. There are three circumstances that influaction. It is obvious that, if the fly be placed ence the electric spark in its passage from one on the upper part of the wires, it will roll down conductor to another, namely, the form of the them by its own gravity; but when it has reached conductors, their extent, and the nature and the bottom of the plane, if the upper end of the density of the medium through which the spark wires be connected with the machine while in passes. The following remarks on these three action, the escape of the fluid from the points circumstances we give nearly in Mr. Singer's will cause it to roll very rapidly up the plane own words. till it reach the top of it. These experiments 102. The distribution of electricity on conmay be varied to a great extent, and models of ductors has but little relation to their solid concorn-mills, water-pumps, astronomical clocks, tents, and depends almost entirely on extent of &c., constructed of cork and pasteboard, are surface, for the same effects are produced by the readily put in action by directing against their thinnest cylinder or sphere of metal as by the main wheels a stream of electricity from a strong most compact solid body of the same form and pointed wire inserted into the prime conductor. dimensions; it is probable that the action of in
(4.) By a fine Maxen thread attach a large sulated conductors consists in the ready commudowny feather to the prime conductor of the nication of their electric state to the contiguous machine ; turn the cylinder gently round, and surface of the extensive stratum of air by which the fibres of the feather will repel each other; they are surrounded, and to the facility they preapproach it with a brass ball, or with the closed sent to the discharge of that electrified stratum hand, and it will endeavour to turn itself to- when an uninsulated or differently electrified wards the ball or hand; but present a pointed body is brought near them; for every positively wire to it, and it will instantly shrink from it electrified conductor is surrounded by a positive back on the conductor, as if animated, which atmosphere, and every negative conductor with. arises from its being suddenly deprived of its a negative atmosphere whose densities decrease electricity by the point. This experiment may as the square of their increased distance. Hence be varied by inserting the brass stem of fig. 12, any insulated electrified body will retain its elecinto one of the holes in the prime conductor. trical state until its intersity is sufficient to