, in Physics, is a term applied to those substances, in which the electric fluid can be excited, and accumulated, without transmitting it; and which are therefore called non-conductors. They are also called original Electrics, and Electrics per se.

The word is derived from plextzon, amber, one of the most observable non-conductors. To this class also belong glass, and all vitrifications, even of metals; all precious stones, of which the most transparent are the | best; all resins, and resinous compositions; also sulphur, baked wood, all bituminous substances, wax, silk, cotton, all dry animal substances, as feathers, wool, hair, &c; also paper, white sugar, and sugarcandy; likewise air, oils, chocolate, calces of metals and semi-metals, the ashes of animal and vegetable substances, the rust of metals, all dry vegetable substances, and stones, of which the hardest are the best.

Substances of this kind may be excited, so as to exhibit the Electric appearances of attracting and repelling light bodies, emitting a spark of light, attended with a snapping noise, and yielding a current of air, the sensation of which resembles that of a spider's web drawn over the face, &c, and a smell like that of phosphorus; and this exciting may be either by friction, or by heating and cooling, or by melting, and pouring one melted substance into another.

The term is peculiarly applied to the electric, viz. the globe, or cylinder, &c, used in electrical machines, to collect the electrical matter by rubbing it.

Electrical Air Thermometer, an instrument contrived by Mr. Kinnersley of Philadelphia, and used in determining the effects of the electrical explosion upon air. The description may be seen in Franklin's Letters, &c, pa. 389, 4to, 1769.

Electrical Apparatus, consists of glass tubes, about 3 feet long, and an inch and a half in diameter, one of which should be closed at one end, and furnished at the other end with a brass cap and stop-cock, to rarefy or condense the inclosed air; sticks of sealing wax, or tubes of rough glass, or glass tubes covered with sealing-wax, or cylinders of baked wood for producing the negative electricity; with proper rubbers, as black oiled silk, with amalgam upon it for the former, and soft new flannel, or hare skins, or cat skins, tanned with the hair on, for the latter; coated jars, or plates of glass, either single, or combined in a battery, for accumulating electricity; metal rods, as dischargers; an electrical machine; electrometers, and insulated stools, supported by pillars of glass, covered with sealing-wax, or baked wood, varnished or boiled in linseed oil.

Electrical Atmosphere, is a stream or mass of the Electrical fluid which surrounds an excited or electrified body, to some distance.

Electrical Balls. See Balls and ELECTROMETER.

Electrical Battery, consists of a large quantity of coated jars, placed near each other in a convenient manner. These being charged, or electrified, and connected with each other, are then suddenly exploded or discharged, with a prodigious effect.

Electrical Fluid, is a fine rare fluid which issues from, and surrounds electrified bodies.

Electrical Kite, was contrived by Dr. Franklin, to verify his hypothesis of the identity of electricity and lightning. It consisted of a large thin silk handkerchief, extended and fastened at the four corners to two slender strips of cedar, and accommodated with a tail, loop, and string, so as to rise in the air like a paper kite. To the top of the upright stick of the cross was fixed a very sharp-pointed wire, rising a foot or more above the wood; and to the end of the twine, next the hand, a silk ribband was tied. From a key suspended at the junction of the twine and silk, when the kite is raised during a thunder-storm, a phial may be charged, and electric fire collected, as is usually done by means of a rubbed glass tube or globe. Philos. Trans. vol. 47, pa. 565, or Franklin's Letters, pa. 111 and 112.

Kites made of paper, covered with varnish, or with well boiled linseed oil, to preserve them from the rain, with a stick and cane bow, like the common ones used by boys, will answer the purpose extremely well, and are very useful in determining the electricity of the atmosphere. See Conductor.

Electrical Machine, is a part of the Electrical apparatus, contrived for collecting a great quantity of electricity, and exhibiting its effects in a very sensible manner. It consists of the electric, the moving engine, the rubber, and the prime conductor. In the early state of this science, for the electric, was used sealing-wax, sulphur, or rough glass; but, since the method of insulating the rubber, and so producing negative electricity, was introduced, smooth glass has been used. The form is commonly either that of a globe, or of a cylinder. Each figure has its advantages, and its inconveniences. Dr. Van Marum, a late German writer, has constructed a machine, in which gumlac, in the form of a disc, is used as an electric instead of glass; which has the effect of depending very little on the temperature of the air; described in his Verhandeling over het Electrizeeren, &c, or a Treatise concerning the method of electrifying. Groningen, 1776. But he has since procured some others to be made by Mr. Cuthbertson, a very ingenious artist, of large discs, or round plates of glass: one of these is now placed in Teyler's Museum at Harlem, having two of these glass plates, of 65 inches diameter, excited, on both sides of them, by rubbers of waxed taffaty; with which, effects are produced that are truly astonishing and tremendous. See his Description of this machine, and its effects, published in 4to, at Harlem, 1785, &c.

There have been various contrivances for giving motion to the electric of a machine. The common method is by a wheel turned by a winch or handle; a cord going round a groove in the periphery of the wheel, and over a pulley in the neck of the globe or cylinder. Others have used multiplying wheels, which are easily turned by a winch; and others again make use of a wheel and pinion, or a wheel and endless screw. But Van Marum's machine it seems has the completest movement, its operation being very uniform, and easily worked; it is kept in motion by a weight, which, after being wound up to the height of 12 feet, will continue the motion uniformly for 6 hours; yielding also a negative power, as well as the positive; and the conductors annexed to it serving easily to convey the electrical power wherever it is required, without the addition of any chain, or wires, &c.

The Rubber is the next material part of a machine. These were formerly made of red basil skins, stuffed with hair, wool, flax, or bran: Dr. Nooth introduced silk cushions stuffed with hair, over which is laid a piece of leather, rubbed with amalgam, which are better than the others. The rubber may be insulated in any way that best suits the construction of the ma- | chine: and a chain or wire may easily be suspended from it, to communicate with the floor, whenever the insulation is not necessary; and thus positive and negative electricity may be produced at pleasure. Van Marum uses mercury to his rubbers.

The Prime Conductor is another necessary appendage to the Electrical Machine: its use is to receive the electricity from the electric, as it is produced, and accumulate it as in a magazine, ready to be drawn off and employed on all occasions. See Prime Conductor.

Description of the most useful Electrical Machines.

Fig. 1, plate ix, represents Dr. Priestley's Machine, a very extensively useful one, described in his History of Electricity; in which g is the globe, or electric; f the rubber; in the two pillars d, d, of baked wood, are several holes to receive the spindles of different globes or cylinders, several of which may be put on together, to increase the electricity: klm is the prime conductor, being a copper tube, supported on a stand of glass or baked wood.

Fig. 2 is Dr. Watson's Machine, for using several globes at once, to accumulate a great quantity of electricity.

Fig. 3 represents a very portable Electrical Machine invented by Mr. Read, and improved by Mr. Lane. A is the glass cylinder, moved vertically by means of the pulley at the lower end of the axis, the pulley being turned by the large wheel B parallel to the table; there are several pulleys, of different sizes, either of which may be used, according as the motion is required to be quicker or slower. The conductor C is furnished with points to collect the fluid, and is screwed to the wire of a coated jar D. The figure shews also the manner of applying Mr. Lane's electrometer to this machine.

Electrical Machines have of late years undergone some very essential alterations and improvements; both from the suggestions of private electricians, and the inventions of Messrs. Adams, Nairne, and Jones, instrument makers in London; some of which are as follow:

Fig. 4 represents a very convenient machine for practice. The frame of this machine consists of the bottom board ABCD; which, when the machine must be used, is fastened to the table by two metal cramps. EF are two round pillars, of baked wood, which support the cylinder G by the axles of the brass or wooden caps H, turned sometimes by a simple winch I, and sometimes by a pulley and wheel, as in the next fig. The rubber is fixed to a glass pillar K, which is fastened to a wooden basis L at the bottom. The conductor N is usually made of brass or tin japanned, and is insulated by a glass pillar, screwed into a wooden basis or foot, which is most conveniently placed parallel to the cylinder.

Fig. 5 represents an Electrical Machine, with a conductor in the shape of a T; and an improved medical apparatus, where it is necessary to give the shock in the arms.

Fig. 6 shews Mr. Nairne's patent machine for medical purposes. Its glass cylinder is about 7 inches in diameter, and 12 long, with two conductors parallel to it. The rubber is fastened to the conductor R; and consists of a cushion of leather stuffed, having a piece of silk glewed to its under part. The conductors are of tin covered with black lacker, each of them containing a large coated glass jar, and likewise a smaller one, or a coated tube, which are visible when the caps NN are removed. To each conductor is fixed a knob O, for the occasional suspension of a chain to produce positive or negative electricity. That part of the winch C which acts as a lever in turning the cylinder, is of glass. Thus every part of the machine is insulated, the cylinder itself and its brass caps not excepted; by which means very little of the electricity is dissipated, and hence of course the effects are likely to be the more powerful. And to this the inventor has adapted some flexible conducting joints, a discharging electrometer, &c, for the practice of medical electricity.

The large Electrical Machine placed in Teyler' Museum at Harlem, has been partly described above. It was constructed by Mr. John Cuthbertson, an English instrument maker; and it has, for the electric, two glass plates of 65 inches diameter, made of French glass, as this is found to produce the most electricity next to English flint glass, which could not be made of a sufficient size: these plates are set on the same horizontal axis, at the distance of 7 1/2 inches, and are excited by 8 rubbers, each 15 1/2 inches long; and both sides of the plates are covered with a resinous substance to the distance of 16 1/2 inches from the centre, both to strengthen the plates, and to prevent any electricity from being carried off by the axis. Its battery of jars contains 225 square feet of coated surface, and its effects are astonishingly great.

Electrical Phial. See Leyden Phial.

Electrical Rubber. See Electrical Apparatus, and Electrical Machine.

Electrical Shock, is the sudden explosion between the opposite sides of a charged electric; so called because if the discharge be made through the body of an animal, it occasions a sudden motion by the contraction of the muscles through which it passes, accompanied with a disagreeable sensation. The force of this shock is proportioned to the quantity of coated surface, the thinness of the glass, and the power of the machine by which it is charged. Its velocity is almost instantaneous, and it has not been found to take up the least sensible time in passing to the greatest distances.

It has been observed that the Electrical Shock is weakened by being communicated through several persons in contact with one another. Indeed it is obstructed in its passage, even through the best conductors, as it will prefer a short passage through the air to a long one through the most perfect conductors; and if the circuit be interrupted, either by electrics, or very imperfect conductors of a moderate thickness, the shock will rend them in its passage, disperse them in every direction, and exhibit the appearance of a sudden expansion of the air about the centre of the shock. A strong shock made to pass through or over the belly of a muscle, forces it to contract; and sent through a small animal body, deprives it instantly of life, and hastens putrefaction. It gives polarity to magnetic needles, reverses their poles, and produces effects precisely similar, though inferior in degree, to those of lightning.

Electrical Star. See Star. |

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Entry taken from A Mathematical and Philosophical Dictionary, by Charles Hutton, 1796.

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