a great improvement, such as the state of manufacturing industry required. Berthollet's plan consisted in employing chlorine, which possesses a wonderful power of removing vegetable colours. The bleaching-powder, or chloride of lime, as it is usually called, is manufactured by exposing slaked lime to the action of chlorine gas, till as much of the latter is absorbed as the lime is capable of combining with under these circumstances. The chlorine in the bleaching-powder, which is not applied till after sundry preparatory washings of the cloth, acts upon vegetable substances by dissolving their hydrogen, which is the colouring agent; the air would have the same effect, but would require a much longer time than can be allowed. The cloth is left in a cold solution of the bleaching-powder for about six hours, and is then taken out and washed with water. The next part of the process is called souring, which is immersing the cloth in a solution of sulphuric acid, so diluted that it does not injure the texture of the goods, whilst it improves their colour. The sulphuric acid dissolves and removes the oxide of iron with which the cloth is always contaminated; it also removes the lime which may have attached itself to the cloth during its previous treatment with that substance. It is again washed, boiled in an alkaline ley, and once more carefully washed in cold water. Another solution of bleaching-powder, two-thirds the strength of the former, is then prepared, in which the cloth is immersed, and left for five or six hours; it finally undergoes another process of souring, by which means it is rendered perfectly white. The acid is carefully removed by washing; and after each piece of cloth has been stretched to its full length, it undergoes a process of mangling, by being passed successively between cylinders forced towards cach other by levers, to which a considerable weight is attached. The cloth being thus stretched, smoothed, and wound upon a roller, is rendered fit for starching. The starch is that of flour, deprived of its gluten by remaining for twenty-four hours in water, and then passed through a sieve, which retains the bran, and allows the starch to pass. A little indigo is mixed with it, and sometimes porcelain clay. The starch is applied in the state of a pretty thick paste whilst the cloth is passing between a pair of rollers. The goods are then dried and passed through a calender for the purpose of giving them a gloss and texture. Such is the process of bleaching as practised in the large bleaching establishments on the common class of goods. The number of processes which the cloth undergoes amounts to about twenty-five, but some of the earlier ones are occasionally omitted. The expense of bleaching and finishing a yard of cotton cloth is about one halfpenny, and the time required is trifling. A Bleacher in Lancashire, we are told, received fourteen hundred pieces of grey muslin on a Tuesday, which on the Thursday following were returned bleached to the manufacturers, at the distance of sixteen miles; and on the same day they were packed up and sent to a foreign market. CONDIMENTS. Sugar-Salt. Two of the most important condiments in domestic use are, as is well known, sugar and salt; both of which substances are the crystallisation of liquids loaded with their respective properties: each is produced by an evaporation of the watery particles, leaving the solid crystals behind. Thus, sugar is a crystallisation of the juice of the sugar-cane, beet-root, or other vegetables containing saccharine matter; the residuum or uncrystallisable material being that viscid and sweet fluid called treacle. Salt, called by the chemists the muriate of soda, or chloride of sodium, is found to exist in a natural state in various quarters of the globe, among others, in the county of Cheshire in England, where it is dug from a mine, and purified by being mixed with water and subjected to evaporation. The principal source of salt, however, is the water of the ocean, which is boiled for rtain length of time, to drive off the watery par ticles. Sea-water differs in strength; that which con tains the largest quantity of salt being in the middle of the ocean, far from the mouths of rivers. From 38 to 43 per cent. is the quantity commonly found in the seas round our coasts. The method of making salt is simple; but from the length of time required in boiling, it is not economically performed unless near mines from which coal can be cheaply procured. The plan pursued is to erect a reservoir near the sea, into which at high water supplies are taken by means of a pipe extending a good way down the beach. The pipe is generally placed near the low-water mark, in order to get the water from a point as far from the surface as possible, so that it may be the more impregnated with salt, and require less boiling. The pans are built on a range on both sides of the reservoir, from which the water is pumped into them after the impurities have settled. The pans are shallow vessels, made of sheet iron, about twenty feet long and twelve broad, with a furnace below. These are contained in a small low-roofed house, the covering of which is of deals, with an opening at the meeting of the roof and the wall, to allow the vapour to escape. When the water is boiling, a little bullock's blood is put into the pan, which brings the impurities to the surface and allows of their being skimmed off. As the water boils down, more is pumped in; and this process is repeated before the salt is finally drawn. From a pan of 1300 gallons fifteen or twenty bushels, of fifty-six pounds each, are obtained in this manner, the process requir ing about twenty-four hours. The salt is at first very light and floury in proportion to its bulk, and in this state is most appreciated. A still finer article, resolv. ing into large crystals, is made with a low fire, and when a longer time is allowed in the evaporation. For use at table, the salt is refined, and usually run into large lumps. The water which remains after the salt is crystallised, called the mother-water, contains a considerable quantity of the chloride of magnesium or bittern, chloride of sodium, and sulphate of magnesia. If the mother-water is exposed in tanks during winter, it will afford three successive crystalline deposits, the last of which is sulphate of soda nearly in a pure state. The chloride of magnesium deteriorates the salt very much, but may be removed by the following simple expedient, mentioned by Dr Ure :-" Let quicklime be introduced in equivalent quantity to the magnesia present, and it will precipitate this earth, and form chloride of calcium, which will immediately react upon the sulphate of soda in the mother-water, producing sulphate of lime and chloride of sodium. The former being nearly insoluble, is easily separated. Lime, morcover, decomposes directly the chloride of magnesium, but with the effect of merely substituting chloride of calcium in its stead. But in general there is abundance of sulphate of soda in brine springs to decompose the chloride of calcium. A still better mode of proceeding with sea-water would be to add to it in the settling tank the quantity of lime equivalent to the magnesia, whereby an available deposit of this earth would be obtained, at the same time that the brine would be sweetened. Water thus purified may be safely crystallised by rapid evaporation." The finest table-salt is made in the western parts of England, from the produce of the salt mines; and, along with salt of a common quality, is exported in immense quantities. In 1836, 240,560 tons of salt were exported from the United Kingdom, the greater part of which went to the United States, Russia, Belgium, the British North American Colonies, the West Indies, &c. M. Desormes calculates that the internal consumption of salt in France is rather more than 200,000 tons annually, which is about fourteen pounds for each indi vidual. In this country it is thought to be about 240,000 tons annually, which is upwards of twenty pounds for each individual. Printed and published by W. and R. CHAMBERS, Edinburgh. Sold also by W. S. Orr and Co., London. CHAMBERS'S INFORMATION FOR THE PEOPLE. CONDUCTED BY WILLIAM AND ROBERT CHAMBERS, EDITORS OF CHAMBERS'S NUMBER 57. NEW AND IMPROVED SERIES. ELECTRICITY-GALVANISM-ELECTRO-MAGNETISM. PRICE lad. ELECTRICITY. EXCITATION OF ELECTRICITY, AND RESULTING PHENOMENA. If a piece of sealing-wax, amber, the glass of a watch, or any other smooth piece of glass, be rubbed upon a piece of dry flannel or woollen cloth, or even the sleeve of a cloth coat, it will be found to have acquired a new and very singular physical property. This property is exhibited by holding the body which has been subjected to friction, over small and light substances, such as shreds of paper, gold leaf, feathers, straw, cork, &c. These will be first instantly attracted to it, some of them adhering to its surface, others falling back to the place whence they were withdrawn, whilst others are thrown off from the body as if they were repelled from it. Here, then, is a distinct phenomenon-a process of attraction and repulsion at the same instant of time, which requires careful examination. It is observed, as above stated, that only certain substances will become endowed with these remarkable properties, and for convenience such are called electrics; those which cannot be excited in the same manner are said to be non-electrics: for example, stone is a non-electric. It was observed in ancient times, that, when amber as rubbed, it acquired a power of attracting and reelling such light bodies as hair and feathers; and this wer afterwards came to be called ELECTRICITY, from tron, the Greek word for amber. Although the sents were thus acquainted with some of the more vious phenomena of electricity, they did not investirate the subject methodically, or attempt any generation of facts into a scientific theory. It was only in dern times, when close reasoning from truths estaed by the evidence of the senses began to be practed by philosophers, that the phenomena connected with electricity assumed the dignity of a science. Dr Seibert, an English physician, made the first step towards generalisation, in the year 1600. He published valuable treatise, in which he observed, that not only her, but various other substances, can by friction be ade to draw light bodies to them. Boyle, Guericke, Newton, and some other philosophers of that period, tributed to extend human knowledge upon this ineresting subject; but the real science of electricity its rise in a later age. About the middle of the *ghteenth century, several very remarkable facts vere ascertained, particularly by Benjamin Franklin, which identified lightning with electricity; but the exsive relations which connect it with so many other partments of physical science were not discovered the present century, nor was their importance til then appreciated. In this short era a new science has arisen, founded on that modification of electricity which is known by the name of GALVANISM. The galFame battery (which will be afterwards described), as instrument for analysing or decomposing chemical ubstances, has connected it with chemistry in the most timate manner. Hence has sprung ELECTRO-CHETRY, one of the connecting branches between remote rsions of the philosophy of nature. ELECTRO-MAG-be repelled instead of being attracted, as in the first V is a still more recently discovered province of ence, and which identifies as one, two powers which Te previously regarded as distinct. The phenomena of attraction and repulsion, may be exemplified in a striking manner by a small apparatus, of which we present a representation, fig. 1. A is a stand bent at its upper extremity, and having a hook to which a fine silk thread is attached, with a very small pith ball at its end, B. Rub an electric-for instance, a dry rod of glass and, on presenting it to the ball B, the ball will be immediately attracted to the glass, and will remain in contact with it. After they remain in contact for a few seconds, if the glass be withdrawn without being touched by the fingers, and again presented to the ball, the latter will Fig. 1. instance. By being touched with the finger, the ball can be deprived of its electricity; and if, after this has been done, we present a piece of sealing-wax in place of the glass formerly employed, the very same phenomena will take place. On the first application, the ball will be attracted; and, on the second, repelled. It is clear, then, in the first place, that both these electrics have the power of attracting another body before they have communicated to it any of their own electricity; and, secondly, that they repel the body after they have communicated to it a portion of their own electricity. As the best method of conveying a clear and at the tame time philosophical view of this interesting science, ve shall, in the first place, independently of all theory, ate the most general and remarkable facts connected ath it. After these have been enumerated, the reader athen be prepared for a review of the theories which ave been advanced for the purpose of explaining pheamena, and for connecting the various facts in the Find The general facts relating to this subject we But a very remarkable circumstance takes place, if nk may be classed under two heads-1st, The Exciwe, after having conveyed electricity to the ball B, by tion of Electricity; and, 2d, The Distribution of Elec- means of excited glass, which was for a moment or tricity. Connected with each of these heads are various two in contact with it, should present to it, after the nomena, which we shall notice as they occur, during former was withdrawn, excited sealing-wax: the ball, the gradual development of the subject. instead of being repelled, as it would have been were the glass again applied, is attracted by the wax. If the experiment be reversed, and the excited wax first presented to the ball, and then the excited glass, the latter will be found to repel the ball. "Hence it follows," says Sir David Brewster,* "that excited glass repels a ball electrified by excited glass. Excited wax repels a ball electrified by excited wax. Excited glass attracts a ball electrified by excited wax. Excited wax attracts a ball electrified by excited glass. From which we conclude, that there are two opposite electricities; namely, that produced by excited glass, to which the name of vitreous or positive electricity has been given; and that produced by excited wax, to which the name of resinous or negative electricity has been given. If, when the pith ball B is electrified either with excited glass or wax, we touch it with a rod of glass, its property of being subsequently attracted or repelled by the excited glass or wax will suffer no change; but if we touch it with a rod of metal, it will lose the electricity which it had received, and will be attracted either by the excited glass or wax, as it was when they were first applied to it. Hence, the rod of glass and the rod of metal possess different properties, the former being incapable, and the latter capable, of carrying off the electricity of the pith ball. The metal is therefore said to be a conductor, and the glass a non-conductor, of electricity." In these experiments, electricity has been produced by friction; but there are other methods of obtaining it, which, however, will be afterwards explained. With regard to attraction and repulsion, a few facts remain to be stated. Some substances remain longer in contact with the electric than others, and two bodies which have both been in contact with the same electric, mutually repel each other. If electrics of considerable size are employed, the phenomena of course are best observed; and if the experiment be performed in a darkened chamber, flashes of bluish light will be seen to extend over the surface of the electric submitted to friction, and which we shall suppose is a cylinder of sealing-wax, sulphur, or glass. Sparks, accompanied also with a sharp snapping sound, will be seen to dart round it in various directions. If a round body, as a metallic ball, be presented to it, and moved from one end to the other, a succession of sparks will be obtained as the ball passes along the surface; and if the knuckle be presented instead of the metallic ball, each spark will be accompanied by a pricking sensation. If the cylinder be brought near to the face, an unpleasant sensation of tickling is felt in the skin, as if it were covered with a cobweb. If a metallic globe be suspended in the air by silk threads, and in that situation rubbed by an electric, it will also become electrical, and exhibit the same properties as an electric. It is essential to the success of this experiment that it be insulated; that is, cut off by means of an electric from all communication with any substance, except the air and the electric which sustains it. The instruments employed in experiments similar to those above described, are termed electroscopes. Besides that one of which a representation has been given, there are various others, all of which are formed upon the same principles. It is now proper to mention the principal electrical substances in nature. They are, amber, gum-lac, resin, sulphur, glass, tale, the precious stones, silk, the fur of most quadrupeds, and almost all vegetable substances (excepting charcoal) which have been thoroughly deprived of moisture, as, for instance, baked wood, and very dry paper. DISTRIBUTION AND TRANSFERENCE. tric, and present to the ball which has thus touched a second ball, which has had no previous communica tion with an electric, we find that these two balls attrac one another, and come into contact. The same action are repeated between this second ball and a third whic may be presented to it; and so on in succession, bu with a continued diminution of intensity. This diminu tion plainly indicates a diminished power, in conse quence, as it would seem, of its being distribute amongst a number of bodies. It is clear, therefor that the unknown power which we have called electri city, can, like heat, be transferred or communicate from one body to another, and that its intensity, lik that of heat, is weakened by being diffused amongst number of bodies. An electrified ball can be deprive of its electricity by being touched with a rod of met of any kind; but if we touch it with glass or wax, will not be carried off. Hence, metals are said to conductors, and glass and wax non-conductors, of ele tricity. Bodies greatly vary in their power of condur tion, and many of them owe it to the water which the contain. The conducting power of any substance de pends on the state of the atmosphere at the time wit regard to humidity, and on the intensity of the electr city employed. The following lists of conductors an non-conductors are by Sir David Brewster, and hav been collected by him from various authors, with gres care. The bodies are placed in the order of their con ducting or non-conducting power; "but it is probable, says Sir David, "that this order would be great! changed, if the bodies were all submitted to a new an uniform examination." List of Conductors.-Silver, copper, lead, gold, bras zine, tin, platina, palladium, iron heated, iron col charcoal well burned, plumbago, concentrated acid powdered charcoal, diluted acids, saline solutions, m tallic ores, animal fluids, hot water, sea-water, spring water, river-water, ice above 13 degrees Fahr., snow living vegetables, living animals, flame, smoke, steau soluble salts, rarefied air, vapour of alcohol, vapour ether, moist earths, anthracite, powdered glass, flower of sulphur, resins rendered fluid by heat, glass heate to redness. List of Non-Conductors.-Shell-lac, amber, resin sulphur, wax, jet, glass, vitrifications, mica, diamon transparent gems, various minerals, raw silk, bleach silk, dyed silk, wool, hair, feathers, dry paper, parch ment, leather, air and all dry gases, baked wood, dr vegetable bodies, porcelain, dry marble, and silice and argillaceous stones, camphor, caoutchouc, lycope dium, dry chalk, lime, phosphorus, ice below 13 de grees Fahr., ashes of animal bodies, ashes of vegetal bodies, oils (the heaviest being the best conductors), dr metallic oxides. The two qualities of a capability of excitation, an a power of conducting electricity, appear to be incor patible with each other, for the one always diminishe in proportion as the other increases. Hence it fo lows, as an invariable law, that electrics are non-com ductors, and, on the other hand, that conductors ar non-electrics. The most perfect non-conductors electricity are also called insulators, from their powe of insulating an electrified body, or preventing any its electricity from escaping along its support. Th insulating power of atmospheric air depends upon t circumstances-its density and its dryness. Air of th ordinary density of the atmosphere, if perfectly dry is a remarkably good insulator, and no change of ten perature appears to affect its insulating power; h rarefaction diminishes its power of confining electricity and, when greatly rarefied, it may be classed among conductors. The conducting power of air of the ord nary density depends upon the quantity of moistur which it contains, water being a very good conductor We have noticed that when the excited electric was brought near the pith ball B, the latter was first at tracted and then repelled. If we now remove the elec-electricity. Changes of temperature and also of for * Article Electricity in the Encyclopædia Britannica, the most crehensive, philosophical, complete, and intelligible treatise tais interesting science which we have ever yet met with. 98 affect the conducting powers of most bodies. Thu though water, in its ordinary liquid state, is an exce lent conductor, yet, when it appears in the solid form ice, its conducting power is much impaired, and at very low temperature it ceases entirely. Glass, when | 1. All bodies conduct electricity in the same manner, rm metals to lac and gases, but in different degrees. Conducting power is in some bodies powerfully incased by heat, and in others diminished, yet without perceiving any accompanying essential electrical ference, either in the bodies or in the changes occaned by the electricity conducted. A number of bodies insulating electricity of low Ensity when solid, conduct it very freely when fluid, are then decomposed by it. 4. There are many fluid bodies which do not sensibly duft electricity of this low intensity; there are some ach conduct it and are not decomposed, nor is fluidity sential to decomposition. 5. There is but one body yet discovered (periodide 4 mercury), which, insulating a voltaic current when d and conducting it when fluid, is not decomposed Le latter case. There is no strict electrical distinction of contors which can as yet be drawn between bodies posed to be elementary, and those known to be com nds. There are various other circumstances upon which conducting power of bodies depends. That of silk, ir instance, is affected by the colour of the thread, or her by the nature of the dye-stuff by which it has a tinged. When of a brilliant white, or a black, its ducting power is the greatest; and a high golden w or a nut-brown renders it the best insulator. Ar Coulomb, who has investigated the subject with great ability, assigns three causes as chiefly operating depriving a body in a state of imperfect insulation of electricity-first, the imperfection of the insulating perty in the solids by which it is supported ; secondly, contact of successive portions of atmospheric air, ry particle of which deprives the body of a portion ta electricity; thirdly, the deposition of moisture on the surface of the insulating body, which estades communications with its remote ends, thus virAly increasing its conducting power. There is anvery remarkable circumstance relating to the pation of electricity, namely, the shape of the body ach holds the electricity. Its retaining power is Laterally affected by the form which it possesses. The meal shape is that most favourable to its retention; t, from bodies of a pointed figure, especially if the projects to a distance from the surface, electricity apes most readily. On the other hand, these bodies electricity more readily than those of any other " OF THE TWO KINDS OF ELECTRICITY. pelled by the one, are attracted by the other. Of course, these two surfaces, having acquired opposite electricities, invariably attract each other. A white and a black ribbon rubbed against each other between the finger and thumb, exhibit electrical phenomena in a very marked manner. The black is resinously and the white vitreously electrified; of course, they attract each other; and, if separated, the one attracts the light bodies which the other repels. When two pieces of the same ribbon of the same length are rubbed, the one being drawn lengthways and at right angles over a part of the other, the one which has been subjected to friction in its whole length, acquires vitreous and the other resinous electricity. In like manner, when the whole length of the bow of a violin is drawn over a limited part of the string, the hairs of the former exhibit a vitreous, and the latter a resinous electricity. It is to be observed, that the body whose excited portion is of the least extent, is generally found to be resinously electrified. To know the species of electricity evolved, it is merely necessary to communicate beforehand, to the slips of gold leaf, a known electricity, either from excited glass or sealing-wax. If they be divergent with the former, then the approach of a body similarly electrified will augment the divergence, but that of one oppositely electrified will cause their collapse. No visible relation can be pointed out between the nature or constitution of substances, and the species of electricity developed by their mutual friction. The only general law among the phenomena is, that the rubbing and the rubbed body always acquire opposite electricities. Sulphur is vitreously electrified when rubbed with every metal except lead, and resinously with lead and every other kind of rubber. Resinous bodies rubbed against each other acquire alternately the vitreous and resinous electricity; but rubbed against all other bodies, they become resinously electrical. White silk acquires vitreous electricity with black silk, metals, and black cloth; and resinous with paper, the human hand, hair, and weasel's skin. Black silk becomes vitreously electrical with sealing-wax, but resinously with hares', weasels', and ferrets' skins; with brass, silver, iron, the human hand, and white silk. Woollen cloth is strongly vitreous with zinc and bismuth; moderately so with silver, copper, lead, and specular iron. It is resinous with platina, gold, tin, antimony, grey copper, sulphuret of copper, bisulphuret of copper, sulphurets of silver, antimony, and iron. Dry air impelled on glass becomes resinously electrical, and leaves the glass in the opposite state. Silk stuffs agitated in the atmosphere with a rapid motion, always take the resinous electricity, while the air becomes vitreously electrified. Numerous experiments have been made with the view of ascertaining the conditions that determine the species of electricity exerted in the respective bodies of which the surfaces are made to rub against each other, but they have led to no satisfactory conclusions. The mechanical configuration of the surface appears to have a greater influence in the result than the peculiar nature of the substance itself. If a plate of glass with a polished surface be rubbed against one which is roughened, the former always acquires the vitreous and the latter the resinous electricity. Various substances, if rubbed when polished, exhibit a different kind of electricity than that with which they are excited, if rubbed when roughened or scratched. No purely scientific explanation has ever yet been given of these remarkable phenomena. will be understood, from the preceding explana, that there are two kinds of electricity-namely, treous or positive electricity, and a resinous or ante electricity. Although we have thus two elecis, there does not appear to be the smallest diffebetween them when they are taken individually. distinction is only observable when brought in act; they then display so marked a contrariety, or ally opposive force, that they may be viewed as nts having opposite qualities, which completely neu- If a body is charged with electricity, and insulated one another by combination, just like an acid so perfectly as to prevent the escape of the electricity dan alkali. It is remarkable that the excitation which it contains, it nevertheless tends to produce an ne species of electricity is always accompanied by electrical state of the opposite kind in all the bodies the presence of the other, and both are produced to around it. Thus the vitreous induces the resinous, A equal extent. Thus, when a piece of glass is rubbed and the resinous the vitreous electricity in a body lk, just as much resinous electricity is produced that is situated in the vicinity of either of them, and a the silk as there is vitreous electricity produced this to a degree proportioned to the smallness of the the glass; and whatever electrified bodies are re-distance which separates the bodies. The electricity 99 is in this case said to be induced, and the phenomenon | a compound, susceptible of decomposition by friction is called electrical induction. The operation of this law and other means; and hence the origin of the terms is a key to the principal phenomena of electricity. In vitreous and resinous electricities. With respect to the illustration of it, we shall quote an able writer upon intensity of the electric force, it resembles that of grathe subject:-" If an electrified body, charged with vitation, by being inversely as the square of the diseither species of electricity, be presented to an unelec- tance. Like gravitation, also, it acts at all distances, trified or neutral body, its tendency, in consequence of and it is not impeded by any intervening body, provided the law of induction, is to disturb the electrical condi- it be not in an active electrical state. But whilst the tion of the different parts of the neutral body. The particles of each fluid repel those of the same kind, they electrified body induces a state of electricity contrary exert, as we have seen, a high attractive power over to its own in that part of the neutral body which is those of an opposite kind. The intensity of this attracnearest to it; and, consequently, a state of electricity tion, also, like that of gravitation, increases with a disimilar to its own in the remote part. Hence, the neu- minution of distance. It is evident, therefore, that from trality of the second body is destroyed by the action of the powerful attraction which they have for each other, the first; and the adjacent parts of the two bodies, they would always flow towards each other and coalesce, having now opposite electricities, will attract each other. were it not that the non-conducting properties of elecIt thus appears that the attraction which is observed to trics offer an impediment to their motion. When these take place between electrified bodies, and those that are obstacles are removed, they immediately rush into unelectrified, is merely a consequence of the altered union, and give rise to the remarkable phenomena state of those bodies, resulting directly from the law of already noticed. induction; and that it is by no means itself an original law or primary fact in the science. The effect of induction will be in proportion to the facility with which changes in the distribution of electricity among the different parts of a body can be effected, a facility which corresponds with the conducting power of the body. Hence, the attraction exerted by an electrified body upon another body previously neutral, will be much more energetic if the latter be a conductor than if it be an electric, in which these changes can take place only to a very small extent. This is confirmed by the following experiment :-Suspend, by fine silk threads of equal length, two small balls of equal dimensions, both made of gum-lac, but one having its surface covered with gold leaf. Place these two pendulums, as they may be called, at a little distance from one another, so as to admit of a comparison of their motions; and then present to them an excited electric, which may be either a tube of glass or a cylinder of sealing-wax. It will at once be seen that the ball with the metallic covering, which readily admits of the transfer of electricity from one side to the other, will be much more readily and powerfully attracted than the other ball, which allows of no motion in its electricity. The latter ball will, by slow degrees however, assume electrical states of the same kind as the gilt ball, and will be fully attracted. As this change is very slowly effected, so it is more permanent when once produced; and the plain ball adheres for a considerable time to the electric which has attracted it. The gilt ball, on the contrary, is sooner repelled, by its readily receiving the charge of electricity imparted to it by the electric. A degree of permanent electricity, however, is also induced on this ball, in consequence of its gradual penetration into the substance of the gum-lac." Electrical phenomena are generally accounted for by supposing that there is an extremely subtile and highly elastic fluid, which pervades all material substances, but is itself devoid of any sensible gravity. It is supposed to move with various degrees of facility through the pores or actual substance of various kinds of matter. Hence, in proportion as they admit of the fluid passing through them with ease or difficulty, bodies have been divided into conductors and nonconductors. According to the doctrine of there being but one species of fluid, it is supposed that the electrical equilibrium which constitutes the natural state of matter is disturbed by friction, and that one of the two bodies brought near to each other, attracts to itself a surcharge of the fluid, and is over-saturated, whilst the other is left in a deficient state, and is under-saturated. For this view of the subject we are indebted to Franklin; and hence the terms of positive or plus, and negative or minus, have arisen." But as some f the appearances cannot easily be reconciled to the thesis of a mere excess or deficiency of one fluid, is another theory which supposes the fluid to be ELECTRICAL MACHINES. Rubbing or friction, it will be perceived, is always requisite to produce an artificial display of electrical phenomena. Thus, in rubbing the back of a cat, in rapidly drawing off a silk from a woollen stocking, or in performing any similar action with suitable, and in all cases dry, substances, we evolve electric sparks, of lesser or greater intensity. For the purpose of produe ing powerful electrical results, the aid of mechanism has been found essential. There are various kinds of electrical machines, but all constructed on similar prin ciples. We here offer a representation of that which i most commonly used, in our description of which, the essential parts constituting such instruments will appear A B, fig. 2, is a hollow cylinder of polished gla which revolves upon a horizontal axis, and is from eig to sixteen inches diameter, and from one to two f long. For the purpose of insulation, it is suppor on two upright pillars of glass, which are fixed in wooden stand. Two hollow metallic conductors, eq in length to the cylinder, and about one-fourth of diameter, are placed parallel to it, one on each si upon two insulating pillars of glass, which are cemen into two separate pieces of wood, that slide across base, so as to allow of being brought within differ distances of the cylinder. To one of these conduct the cushion is attached, which is of the same len with the conductor C. The cushion is usually mad soft shammy leather, stuffed with hair or wool, so a be as hard as the bottom of a chair, but yet sufficie yielding to accommodate itself, without much press to the surface of the glass to which it is applied. prime conductor is a cylindrical tube, each end ter nating in a hemisphere. As the electricity is only tained at the surfaces, it is made hollow, generall thin sheet brass, copper, tin, or pasteboard covered |