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46. Of the first kind, viz. friction, the instances are most numerous, and, as Mr. Singer remarks, under certain limitations, universal; they may indeed be obtained by rubbing any of an extensive list of resinous and silicious substances; and of dry, vegetable, animal, and mineral productions. The electricity thus excited, is most readily rendered visible by its effects on the gold leaf electrometer.

47. Examples of the second kind are also very numerous. If a small quantity of sulphur be melted and poured into a conical wine glass, it will contract a little, and become electrical in cooling. A silk thread with a small hook at the end of it, or a rod of glass should be inserted in the sulphur while in a fluid state, to serve as a handle for separating it from the glass when cold. On being separated from the glass, the sulphur will exhibit other signs of electricity; if kept in the glass it will retain its electric virtue for years, and evince it very perceptibly on every attempt to separate the two substances.

48. Mr. Henly discovered that chocolate, fresh from the mill, becomes strongly electrical, as it cools in the tin pans. It soon loses this property, but recovers it once or twice, by being melted in an iron ladle and poured into the tin pans. When the mass becomes dry, the electricity cannot be restored by melting, unless olive oil be mixed with it in the ladle; in which case it completely recovers its electric power. M. Chaptal observed the same circumstance during the congelation of glacial phosphoric acid. Calomel also, when it fixes by sublimation to the upper part of a glass vessel, has been found strongly electrical. The condensation of vapor, and the evaporation of fluids, though apparently opposite processes, are alike sources of electrical excitation.

49. Various crystallised gems,. and a stone called the Tourmalin, become electrical by the mere application of heat; but no other substances have yet unequivocally manifested the same property; though the effects of friction are generally increased, if it is preceded by a moderate elevation of temperature.

50. The contact of dissimilar bodies is proably in all cases the real primary cause of electrical excitement, but it is rarely employed alone, for electricity is known to us only by its effects, which are constantly the result of an artificial arrangement, and consequently may not immediately succeed the primary cause of electric powers, similar in their separate action on the electrometer, and other indifferent matter; but everting a mutual influence on each other, destructive of their individual properties.

51. It was at first supposed that these phenomena were peculiar to the substances by which they were produced; hence the power excited by the friction of glass was termed vitreous electricity; and that by the friction of sealing-wax, resinous electricity. It has, however, long since been proved that both powers are produced in every case of electrical excitation; and, because their mutual counteraction of effect resembles that of an affirmative and negative power, they have been styled positive and negative electricity. 52. The determination of these two states of electricity in different excited bodies, continues

Mr. Singer, is of importance to the practical electrician, and may be thus effected :-Sealingwax when rubbed on woollen cloth is negatively electrified. Glass, when rubbed with silk is positively electrified. Let an electrometer he made to diverge by its being approached by an excited stick of sealing-wax: while in this state, approach it with any excited body, the electricity of which is to be determined. If the divergence of the electrometer increase, the presented body is negative; if it be diminished, the presented body is positive. In other words, all those substances that lessen the divergence occasioned by excited wax, are positive; and such as increase it, negative: whilst those which lessen the divergence produced by excited glass, are negative; and such as increase it positive. Examining, by this test, the effects produced in some of the instances of excitation already considered, we find the truth of the preceding statements, and the relation of the different electrical states to the processes by which they are produced, become more intelligible. Care ought to be taken to destroy the divergence of the electrometer after every experiment of this nature; this is best effected by touching its cap with one end of a piece of brass wire.

53. As an illustration of the doctrine here advanced let the following simple and easily performed experiments be made.

(1.) Roll up a warm and dry piece of flannel, so that it may be held by one extremity, while a stick of sealing-wax is rubbed with the other. After a slight friction present the flannel to an electrometer, which will instantly diverge; while this divergence continues, bring the stick of sealing-wax near the cap, and the leaves of the electrometer will quickly collapse. Both these substances, it is obvious, are electrified by mutual friction, but their electricities are opposite, that of the wax being negative, and that of the flannel positive.

(2.) The electricities thus produced are equal to each other: for if the friction be repeated, and the two substances be both presented to the electrometer at the same time, no signs of electricity appear: the opposite electricities, when applied together, producing a reciprocal counteraction of effect.

(3.) If a black and a white silk riband be excited in contact, in the manner already described, the black riband will be found to be negatively, and the white one positively electrified.

(4.) Take the sulphur cone described at 47, apply it and the glass separately to the electrometer; the cone will be found to be negatively and the glass positively electrified.

54. From the above experiments it appears, that in all cases of excitation positive and negative electricity are produced at the same time, and may be observed by the use of proper means. But it also appears that by friction with the same substance, different bodies are variously affected; for glass rubbed with silk evinces positive electricity: but wax rubbed with silk is rendered negative. Again, polished glass, when rubbed with silk, skin-wool, or metal, becomes positive; but if it be excited by friction against the back of a living cat, it appears negative. Wool, silk,

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or fur, rubbed against sealing-wax, are rendered positive; but gold, silver, or tin, are by the same process rendered negative.

55. Electricians have drawn up tables for

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showing at one view what kind of electricity
will be produced by rubbing various electrics
with different substances; the following Mr.
Singer gives us on the authority of Mr. Cavallo.
By friction with

Every substance with which it has been hitherto tried.
Every substance hitherto tried, except the back of a cat.
Dry oiled silk, sulphur, metals.

Woollen cloth, quills, wood, paper, sealing-wax, white-
wax, the human hand.

Amber, blast of air from bellows.

Diamonds, the human hand.

Metals, silk, loadstone, leather, hand, paper, baked wood.

Other finer furs.

Black silk, metals, black cloth.
Paper, hand, hair, weasel's skin.
Sealing-wax.

Hare's, weasel's, and ferret's skin, loadstone, brass, silver,
iron, hand, white silk.

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In a note appended to the preceding table Mr. Singer says, Mr. Cavallo had inserted metals, which appeared to imply that the friction of all metals electrified sealing-wax positively; this I find is not the case: iron, steel, plumbago, lead, and bismuth, render sealing-wax negative, and all the other metals I have tried leave it positive. I have therefore made a slight alteration in the table. The least difference in the conditions of such experiments will occasion singular varieties of result: with the same rubber (an iron chain), positive electricity may be excited in one stick of sealing-wax, and negative in another, if the former have its surface scratched, and the latter be perfectly smooth. Many repetitions of each experiment are therefore essential to an accurate conclusion.

56. The result of experiments of the kind just described, Mr. Singer found to be much influenced by the state of the bodies employed, and the manner in which the friction was applied to them. In general, he remarks, strong electric signs can only be produced by the friction of dissimilar bodies; but similar substances, when rubbed together so that the motion they individually experience is unequal, are sometimes electrified; and, in such cases, the substance of which the friction is limited to the least extent of surface, is usually negative. This he farther remarks is the case with the strings of a violin, over a limited part of which the bow passes in its whole length, and the hairs of the bow become positive.

57. From these facts he draws the following conclusions, viz. that positive and negative electricity are concomitant phenomena, and that in all cases of electrical excitement, they are both produced, though one only may occasionally appear; and that these phenomena are not peculiar to any distinct class of bodies, but may be produced alternately in various substances, by changing the materials or method by which friction is communicated to them.

THE COMMUNICATION OF ELECTRICITY. 58. Mr. Cavallo, speaking of communicated electricity, remarks, that under such a title falls almost all that we know of the subject: the passage of this virtue, says he, from one body to another is what causes its light; by being communicated to other bodies we see its attraction; by its quick transition it melts metals, destroys animal and vegetable life; and, in short, it is by this communication that the science is known and cultivated.

The following observations and experiments on this particular part of the subject we give from Mr. Singer, with a few necessary exceptions, preferring them to any thing we have yet seen for their appropriateness and concise

ness.

59. From the few simple experiments which we have already described the reader must be aware that electricity can be communicated or conveyed from one body to another. But the faculty of electrical transmission is very different in different bodies; some convey it with great rapidity; others more slowly; and there are some that appear absolutely to arrest its progress. Examples of this fact are apparent in the most simple experiments. The divergence of an electrified electrometer may be destroyed, weakened, or maintained, by touching its cap with different bodies; now, as the divergence of the electrometer is caused by its electricity, such effects can only be produced by the relative power of the touching bodies to deprive it thereof; for so long as the electricity remains the divergence will continue unaltered.

60. This may be shown most satisfactorily by the two following experiments. (1.) Touch the cap of the electrified electrometer with a stick of dry glass, sulphur, or sealing-wax; the divergence of its leaves will continue; this shows therefore that these substances do not transmit electricity. (2.) Touch the cap of the electrified electrometer with a piece of wood, a rod of

any metal, a green leaf, or with the point of the finger; its divergence immediately ceases. Such bodies therefore permit the transmission of electricity.

61. By experiments of this kind it is found, that there is a gradation of effect from one class of bodies to the other. Those which transmit electricity with facility are called conductors; those whose transmitting powers are inferior, imperfect conductors; and such as have no power of transmission, non-conductors: but in general the various bodies in nature are divided into two classes only; the remote extremes of each forming the intermediate class.

62. In the following enumeration of the principal conductors, and non-conductors, the substances are placed nearly in the order of their perfection; but the determination of this circumstance has not hitherto been accomplished with much precision.

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The diamond and all transparent gems.
Raw silk, bleached silk, dyed silk.
Wool, hair, feathers..

Dry paper, parchment, and leather.
Air, and all dry gases.

Baked wood, dry vegetable substances.
Porcelain, dry marble.

Some silicious and argillaceous stones.
Camphor, elastic gum, lycopodium.
Native carbonate of barytes.

Dry chalk, lime, phosphorus.
Ice at 13° of Fahrenheit.

Many transparent crystals when perfectly dry,
Ashes of animal bodies.
Ashes of vegetable bodies.
Oils, the heaviest are the best.
Dry metallic oxides.

65. The most perfect non-conductors, continues Mr. Singer, become conductors by the accession of moisture; hence the necessity of preserving them clean and dry during electrical experiments. Resinous substances, raw silk, and Muscovy talc, are least liable to attract moisture, and are therefore most useful where perfect nonconductors are required.

66. Glass (becomes moist on its surface only, and this moisture may be checked by covering it with sealing-wax or good varnish. Glass consequently enters most extensively into the structure of an electrical apparatus; its strength, and the facility with which it may be procured of any form, fitting it most admirably for that purpose.

67. Many substances in the preceding list lose their non-conducting power, and become conductors, when intensely heated. Such is the case with red hot glass, melted resin, wax, &c.; but the most intensely heated air, if unaccompanied by flame, is not a conductor. Many fibrous substances attract water so readily, that it is absolutely necessary to dry and warm them before their non-conducting property appears; this is particularly the case with paper, flannel, parchment, leather, &c. The influence of heat on this property is, indeed, very remarkable. It is well exemplified in the following instance: Wood, in its natural state, is a conductor; if baked, its moisture is expelled, but its organisation is not altered: it is then a non-conductor. By exposure to a greater heat its volatile elements are dissipated, and its indestructible base (charcoal replete with alkali) only remains; this is a conductor; but if exposed again to heat, with access of air, it suffers combustion, and is converted into ashes and gases, which are non-conductors.

68. There does not appear any definite relation between the chemical characters of bodies and their conducting powers; for the best conductors (metals), and the best non-conductors (resins, sulphur, &c.), are alike inflammable substances. The products of combustion, too, are dissimilar in this respect: acids and alkalis conduct electricity, but the metallic oxides do not. Neither does it appear that specific gravity, hardness, tenacity, or crystalline arrangement of particles, are connected with the power of electrical transmision; for similar characters of this kind are possessed by bodies of both classes. Thus platina, the densest of bodies, is

a conductor; but so also are charcoal, and rarefied air.

69. Whatever be the cause of non-conducting power, it is evident that without its existence as a property of air, and other substances, electrical phenomena would be unknown; for, if the faculty of electrical transmission existed universally, the cause of every effect of this kind would be dissipated and lost at the moment of its prodaction. But, by the property of non-conductors, any excited electricity which they surround is preserved; and it is then said to be insulated. A support of glass, sealing-wax, silk, or any non-conductor, is, for the same reason, called an insulating support, or an insulator; and a piece of metal or other conductor, so supported, is named an insulated conductor.

70. The use of insulators and conductors in practical electricity may be exemplified by very simple experiments, which, says Mr. Singer, will form no improper introduction to the consideration of more important apparatus. He gives the following:

(1.) Hold a sheet of writing paper before a fire till it be perfectly dry and warm; lay it flat upon a table and rub the upper surface briskly with Indian rubber. The paper will adhere to the table, and if lifted up by one corner and presented quickly to any flat conducting surface, as the wainscot, &c., will be attracted by and adhere to it. This adherence is occasioned by the attraction of electricity excited on the paper, which in its dry state is an insulator or non-conductor; the necessity of which circumstance to the success of the experiment is rendered evident by the paper falling down as soon as it has attracted rroisture enough to destroy its insulating property, and is further apparent from the impossibility of producing the same results by the friction of paper in its ordinary state of dry

ness.

(2.) Repeat the excitation of the paper in a dark room; when the paper is lifted from the table by its corner, present the knuckle of the other hand successively to various parts of its surface, a series of faint divergent flashes of light will ensue. This light is occasioned by the transmission of the electricity excited on the paper to the hand; and it occurs at every contact, because the non-conducting power of the paper prevents its transmission from one part of the surface to another, the effect existing over the whole portion that has been subjected to fric

tion.

(3.) Excite the dry sheet of paper as before, and place it upon an insulating stand, a piece of apparatus to be described hereafter, present the knuckle to the edge or under side of the metal plate, and a bright spark will appear; but a second approach will produce either a very slight effect, or none that is perceptible; for the metal is a conductor, and it transmits the whole effect of the excited electric at once. Hence insulated conductors are employed in the electrical apparatus to receive or collect the diffused electricity of excited bodies, and to apply it to the purposes of experiment.

71. It is rather remarkable that the ingenuity of Mr. Singer did not lead him to try the ex

periments here detailed with brown, as well as writing paper. This idea, however, does not seem to have occurred to writers on the subject till very recently. When very coarse brown paper is used, the effects produced are much stronger; nor is there in this case any necessity for the application of Indian rubber; for if a piece of coarse brown paper, of about twelve inches long and six inches broad, be made very dry and warm, and then drawn gently three or four times between the knee and the lower part of the arm, both being covered with woollen, it will be found to be highly electrical, and will with considerable force adhere to the wainscotting of a room. If any conducting substance be applied to it immediately after the friction, such as the knuckle of the folded hand, or a brass ball, a strong spark will instantly dart from the paper to it, attended by the usual snapping sound. So powerful indeed is excited brown paper, when carefully managed, that a small jar may be charged with it; and it has been recently proposed as a covering for a circular board to be used instead of a plate of glass in constructing a cheap kind of electrical machine.

PART II.

ON ELECTRICAL APPARATUS. 72. Numerous, extremely beautiful, and delicate experiments may be made in electricity with but a small quantity of apparatus, and that of a simple form, and at a trifling expense. Such an apparatus consists chiefly of a few glass tubes, of about an inch in diameter and two or three feet long; one of two very large sticks of sealing-wax; a few pieces of silk, old silk handkerchiefs answer extremely well; a few pieces of new flannel; some wires and balls of different sizes; and half a dozen small balls made of the pith of elder.

But, when it is required to exhibit the more striking and important of the electrical phenomena, we must have recourse to a much more powerful, complicated, and consequently expensive apparatus.

73. The principal article, the very fountain, so to speak, of all electrical apparatus, is what is commonly denominated the electrical machine; of the structure of this instrument we have various accounts in different works on electricity, but as it is not our intention to swell our pages with a repetition of what others have said before us on what is now become obsolete, we shall not put our readers to the trouble of travelling over an uninteresting description of apparatus which has nothing to recommend it but its antiquity.

74. Of the Electrical Machine, there are now various kinds in use; these, however, may be classed under two heads, the cylindrical and the plate machine. But before entering on a particular description of these we feel strongly inclined to lay before our readers the following remarks of Mr. Singer on electrical apparatus in general.

75. The structure of an electrical apparatus, says this distinguished electrician, consists in the judicious arrangement of insulators and conductors, so that the former shall prevent the dissipa

tion of the effects the latter are employed to collect or transmit; thus the cap and leaves of the gold leaf electrometer form a conductor intended as a test of electrical action; but to fit this conductor for its purpose it is insulated, being supported on the glass cylinder by which the leaves are enclosed.

76. When electricity is excited by friction, the quantity of effect is, within certain limits, proportioned to the extent of the rubbed surface; hence it appears that every part of that.surface is concerned in the production of the general effect. Now, that this may be the case, it is essential that every part of such surface be insulating; for friction is a progressive process, a succession of contacts; and the effect produced by it in the first instant would otherwise be destroyed by conducting power, before a second operation could contribute to its increase. For this reason electricity is most usually excited by the friction of a conductor of limited size, against the extensive surface of a non-conductor.

77. An apparatus, then, properly arranged for the excitation of electricity, is called an electrical machine. To excite positive electricity, a glass tube, of about an inch in diameter and two feet long, is generally used; the excitation is produced by rubbing it lengthwise by a piece of dry oiled silk, held in the hand which is made to grasp the tube. In this way both the silk and the tube are electrified; but the electricity of the silk is destroyed by the conducting power of the hand, and that of the tube only appears. In a similar way negative electricity is procured by rubbing a large stick of sealing-wax with dry flannel or fur; the electrical power of the sealing-wax being all that results.

78. Thus, with the most simple machinery, two processes are employed to procure the opposite electricities, although they are at the same time both excited in each; but, to obtain them both, it would be necessary to insulate the silk, or flannel, used as rubbers, either by employing them in a very dry state, rolled up, so as to produce the friction with one extremity, at a distance from the hand, or by affixing them to a glass or other non-conducting support; but neither of these methods would be convenient where many experiments are to be made. This difficulty does not occur when large surfaces of glass are employed instead of tubes as sources of exc tation; for these may be made circular, and proper friction be communicated to them from a fixed cushion, placed on an elastic support, against which they are made to revolve.

79. We shall here give a brief description of the two forms of the electrical machine which are most generally approved of, and shall begin with the cylindrical machine. In point of power, the very best kind of cylindrical electrical machine with which we are acquainted is the improved one, as constructed by the late Mr. Geo. Adams, of London, an eminent lecturer, and author of several valuable philosophical works. This machine is represented in plate I, fig. 1, ELECTRICITY. The parts of the machine, which fall more immediately under our attention are, (1.) The electric, or the glass cylinder which is to be excited. (2.) The mechanical contrivances by which it is put in motion. (3.) The cushion and

its appendages. (4.) The conductor or conductors. The glass cylinder of the machine is put in motion by a simple winch. This is less liable to be out of order than those that are turned with a multiplying wheel, and also enables us to excite the machine more powerfully. The cylinder, FGHI, is supported by two strong perpendicular pieces, DE. The axis of one cap of the cylinder moves in a small hole at the upper part of one of the supports. The opposite axis passes through the upper part of the other support. To this axis the winch or handle is fitted. The cushion is supported and insulated by a glass pillar; the lower part of this pillar is fitted into a wooden socket, to which a regulating screw is adapted, to increase or diminish the pressure of the cushion against the cylinder. A piece of silk comes from the under edge of the cushion, and lies on the cylinder, passing between it and the cushion, and proceeding till it nearly meets the collecting points of the conductor. The more strongly this silk is made to adhere to the cylinder, the stronger is the degree of excitation. Before the cylinder, or opposite to the cushion, is a metallic tube, Y Z, supported by a glass pillar LM. This is called the conductor, and sometimes the prime conductor. For the more conveniently trying experiments with this machine, and exhib.ting the different states of the cushion and conductor, there are two wires to be fixed occasionally, the one to the conductor, the other to the cushion; on the upper part of these are balls furnished with sliding wires, that they may be set apart from each other at different distances.

80. It is matter of surprise that this simple and very powerful electrical machine should have totally escaped the notice of some modern writers on the subject, who have taken much pains to describe others of far inferior importance. This remark is equally applicable to another form of the cylindrical machine which is but little known, but which has many good qualities to recommend it to the attention of those who prefer the cylinder to the plate machine. The principle on which this machine, as well as that just described, is constructed, is that adopted by Mr. Nairne; but whatever of improvement it possesses is due, we believe, to Mr. Bywater, author of an excellent little work on electricity. The following is Mr. Bywater's own description of this machine: AA AA, fig. 2, is the board on which the supporters and pillars are erected, and by which the machine is made fast with cramps to a table. BBBB are two wooden pillars or supporters, the lower ends of which are morticed into the board A A A A, and in the upper ends of which the axis of the cylinder CCCC turns. DD is the winch by which the cylinder is turned on its axis. EE is a piece of wood, a part of which is slided into a groove under the board A A A A, and made fast by the thumb-screw f. GG is a glass pillar, which is fixed to the wood EE, and supports what is called the negative conductor and rubber HH. II is another piece of wood, part of which is slided into a similar groove under the board AAAA, and is made fast by the thumb-screw j. KK is a glass pillar fixed into the wood I I, and supports the prime conductor LL; to this con

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