effect; and not being able to account by friction for the circumstance of two pieces of metal acquiring different electricities in the same flame, according to the temperature. That the effect was not due to the difference of temperature existing in various parts of the same piece of metal, was proved by the entire absence of any electrical phenomena, when a plate of platinum was heated to redness in the focus of M. Fresnel's strong burning-glass. These experiments have some relation to that of M. Volta on the combustion of a piece of amadou at the extremity of a rod communicating with the condensing plate of an electrometer. M. Volta found, that when the apparatus was distant from habitations, the amadou became positive by taking electricity from the circumambient air, from which he concluded that the atmosphere had always an excess of positive electricity. 431. Tin is superior to lead, but the least degree of oxidation renders it inferior. Lead, with zinc, gives greater deviations than tin, iron, brass, or copper. There is no arrangement formed with substances so near to each other, which produces so energetic. a current, and it is in this respect opposed to that presented by zinc, with gold or platina. 432. Charcoal, heated until it ceases to yield flame and slowly cooled, is equal to the metals in electro-motive and conducting power. It does not retard the feeblest electric current. Its electro-motive power is variable, according to the manner in which it is cooled, and also to its exposure to air. 433. Oxide of tin, crystallised, produces currents, with all the metals inferior to it, as zinc, lead, tin, &c.; but none when in communication with bodies having a superior electro-motive force, as gold, silver, carburet of iron, gray ELECTRICAL PHENOMENA ACCOMPANYING COM- manganese, &c.-Annales de Chimie, XXXIII., BUSTION. 426. M. Becquerel found, that on rolling up a sheet of paper, placing it in the electrometer, inflaming it, and touching the flame with a piece of wet wood that the electricity might flow away more rapidly, the paper became positively electrical. If the experiment were inverted, the paper being held in the hand, and the flame made to touch the piece of wet wood placed on the electrometer, it was found that the flame took negative electricity. Hence it may be concluded, that when paper is burnt, the paper becomes positive, and the flame negative. 427. If alcohol be burnt in a copper capsule, it is found by the condenser that the capsule becomes electrified positively. ON THE ELECTRO-MOTIVE FORCE OF CERTAIN SUBSTANCES. 428. Carburet of iron.-In electro-motive power it yields only to certain oxides of manganese. It is augmented by immersion into acidulated water, if the plate be not wiped when withdrawn. This increase of power is not dissipated spontaneously, but is easily lost by the action of an inferior metal, as zinc. When the latter action diminishes that belonging to the carburet, it is resumed spontaneously in a few minutes. The Passau crucibles contain much plumbago, and possess the same properties if the elay has not been too much vitrified; a crucible having an internal surface of 100 square inches, and a vessel of similar form made of thin lead, produced a very useful apparatus. A small interval was left between the leaden vessel and the crucible, and the interval filled with a strong acid solution. By heating the crucible, and cooling the interior of the leaden vessel, important effects, dependent upon the difference of temperature, could be observed. 429. Mercury. This metal ranges between sulphuret of lead and silver; when impure it becomes inferior even to brass, but distillation restores it to its place. 430. Iron.-Its electro-motive power is changed by oxidation, but not much. Its place is always between tin and brass. 136. order of their electro-motive power, the most Charcoal after long exposure to air. Copper pyrites. Lamelliform tellurium. Red silver ore (bright). Arsenical silver, and arsenic slightly oxi- INSULATION OF ELECTRICITY. 435. M. Haüy, in his method of distinguishing precious stones, &c., joins the electric indications given by a gem when rubbed or pressed to its other physical characters. That these indications may be obtained more readily, M. Hauy has invented two smail instruments, very portable, and ready to furnish the two kinds of electricity. One of them is a small bar of Iceland spar, fixed to the end of a needle or lever, which is then suspended by the middle so as to be balanced by a thread of silk. When the spar is pressed between the fingers, it becomes positively electric, and then the electricity of another body, however excited, as of a gem by friction, is ascertained by its attraction or repulsion of the spar. The second instrument is formed of a piece of sealing-wax, flattened at one end so that it may stand on a table, and at the other supporting the point of a needle; a needle of silver or copper, terminated at the extremities by beads, moves on this as on a centre. To charge this apparatus, a piece of amber or sealing-wax is to be excited negatively by friction, and then by touching the needle it becomes similarly electrified, and is then ready to indicate by attraction or repulsion the kind of electricity possessed by another body. 436. M. Hauy has also noticed the extreme permanency of the electrical states of these two apparatuses. His attention was drawn to this circumstance, from the perfection of their action during extremely moist weather, and he was induced to make a few experiments on the subject. The permanency of the electricity excited on the spar depends on the difficulty of adhesion between it and water. In damp weather no moisture deposits on it, so that electricity given to it is perfectly retained. Even if it be dipped in water, and afterwards pressed without wiping, it becomes strongly electric, because no water adheres to its surface to conduct the power away; and M. Hauy at last ascertained that immersion in water was not sufficient to remove electricity previously communicated to it. The permanency, therefore, of its electrical state in the atmosphere, and the value of this property may easily be conceived. If the water be rubbed on the surface of the crystal so as actually to wet it, then no electricity is generated by pressure, and what may have previously been generated is of course dissipated. 437. M. Hauy has observed also, that fluate of lime and the euclax also acquired electricity by pressure, though not so powerfully as Iceland spar; and he found them also to possess similar relations to water. 438. During his experiments on the electricity of minerals, M. Hauy found that the second apparatus also had the power of preserving its electric state unimpaired for a long time; a circumstance scarcely to be expected from its construction. In examining the apparatus, this power was found to depend on the sealing-wax foot, for if that were removed and the needle hung by silk, though it readily took electricity from other bodies, yet it also soon lost it; whereas, on its pivot and foot of sealing-wax, it retained it in damp weather for hours. This appears to depend on a portion of electricity, which, when the needle is first charged, passes on to the surface of the sealing-wax, and, remaining there for a while, gradually returns to the needle, as its state is reduced by the action of the moist air, and supports, as it were, its electricity at a higher tension than it otherwise would have. M. Haüy expresses this by saying that the sealing-wax has the power both of conducting and insulating; by the first it receives a part of the electricity given to the needle, by the second it retains it, and then by the first it gives it back again to the needle when the air has taken away its own portion. The evident conclusion from the experiments is, that the apparatus is always ready for use, and will act in any weather. PLATE ELECTRICAL MACHINES. 439. A variation in the construction of plate electrical machines has been devised and praciced by M. Metzger, of Siblingen, in Schaffhouse, which seems to be a real improvement. Considering that the effect desired in using the machine was first highly to excite the glass, and then to collect the electricity from it, M. Metzger concluded that the distance between the rubber and the points of the conductor, in machines of the common construction, was injurious in its effects, not only by causing the dispersion in part of the electricity excited, but by uselessly wasting the exciting surface. Plates were, therefore, mounted in a very compact and perfect manner, with three pairs of rubbers, placed at equal distances from each other; the conductor also had three arms furnished with points a little in advance of each pair of rubbers, to collect the electricity in the usual manner; and the rubbers were not attached to a surrounding frame, but to brass arms, which, proceeding from a socket through which the axis passes, diverged at equal distances from each other towards the periphery of the plate: the machine has a very compact and neat appearance, and its various smaller parts are contrived with much judgment. 440. In some comparative experiments, made with a plate twenty-two inches in diameter, the superiority of three pairs of cushions over two pairs was very manifest. In the following table the first column expresses the length in inches of the rubbers; the second the length of the spark when two pairs of rubbers were used, and the third the length of the spark when three pairs of rubbers were on the machine. found to adhere so firmly as to support the weight of the slice. The two poles of a tourmaline may also be connected in such a way as to exhibit the effects of attraction and repulsion. To effect which, the oppositely electrified poles are furnished with metallic caps and wires, resembling a horse-shoe magnet; and a light pithball, placed between these metallic conductors, is made to vibrate till the electric equilibrium is restored. ELECTRICITY OF A CAT. 442. The electricity, upon rubbing the back of a cat, is wel! known; and that it is rendered evident by a snapping noise and sparks of light. Mr. Glover, in a letter to the editor of the Philosophical Magazine, describes so intense an action of this kind, as to enable the animal to give a very sensible electric shock. This effect was obtained at pleasure by Mr. Glover, and by some friends. When the cat was sitting on the lap of the person, if the left hand was placed under the throat with the middle finger and the thumb gently pressing the bones of the animal's shoulder, and the right hand was placed along the back, shocks were felt in the left hand; and when the right hand was placed under the throat, whilst the left hand rubbed the back, the shocks were felt in the right hand. When the atmosphere has been favorable, and the cat had lain some time before the fire, the experiment always succeeded. BOINENBERGEN'S ELECTROMETER. 443. This instrument is intended to indicate at once the nature, as well as presence, of electricity. The exterior is formed of a cylinder of glass, about two inches and a half wide: it is closed at the top by a brass plate, from which descend two of De Luc's electric columns, each containing about 400 discs of gilt and silvered paper, about three lines in diameter, and terminated below by brass rings; these tubes are an inch and a half distant from one another, and between them is placed a tube of glass, which, passing through the cover, in the manner of Singer's insulation, supports a wire, terminated below by two gold leaves, and above by a metallic plate. It is easy, from this disposition, to perceive that when the leaves are unelectrified they will hang midway between the tubes; but when affected by the approach of electrified bodies, they will diverge and indicate by the attraction of the leaf on the one side, on the other the nature of the charge. ELECTRICITY PRODUCED BY CONGELATION 444. When water is frozen rapidly in a Leyden jar, the outside coating not being insulated, the jar receives a feeble electrical charge, the inside being positive, the outside negative.' If this ice be rapidly thawed, an inverse result is obtained, the interior becomes negative, and the outside positive.-Grothus. IMPROVEMENT OF THE LEYDEN JAR. 445. M. Metzger has varied the construction of Leyden jars, so as to augment their capacity without increasing their apparent volume. For this purpose, having two jars of proper dimensions, he simply places one within the other, so that they shall apply pretty correctly, and thus have a capacity of charge nearly proportional to the whole surface of coating, without increasing the volume of the whole beyond that of the larger jar. Jars made slightly conical would answer well for this purpose. ELECTRICITY ON SEPARATION OF ARTS. 446. In the water-proof cloths manufactured by M. Mackintosh of Glasgow, where two pieces are cemented together by caoutchouc dissolved in coal, tar, or oil, the adhesion is such, that when the two are torn asunder in the dark, there is a bright flash of electric light, similar to that produced by separating plates of mica, by breaking Rupert's drops, or by breaking barley-sugar, or sugar-candy. Upon trying this experiment with different substances, it was found that flashes of light were distinctly produced by tearing quickly a piece of cotton cloth. ELECTRIC LIGHT. 447. Having a metallic wire covered with silk, form it into a close flat spiral, taking care that the revolutions touch each other: their number may be arbitrary, more than twentyfour have not been used. The properties of this spiral, when it forms part of the Voltaic circuit, are well known; but pass through it a charge of common electricity, such as may be taken by two square feet of coated surface, moderately charged, and a vivid light, something resembling that of an artificial fire-work, will occur, originating from the centre of the spires: it may be seen very distinctly without darkening the chamber where the experiment is made. M. Leopold de Nobili, who describes this experiment, considers the phenomenon as perfectly new. If the wire be folded backwards and forwards, so as to form a rectangular surface, then the electric discharge only produces a faint light at each corner, and this he considers as the light produced by the escape of the electricity into the atmosphere; but the light from the spiral is said to be so vivid and distinct, that once seen, its dissimilarity from the former must be instantly evident; he has therefore called it electro-magnetic light, because of its relation to the magnetic state of the spiral, thinks that it might be made continuous if a sufficiently powerful Voltaic battery were used, and has little doubt but that the aurora borealis is such a light, elicited by the magnetic state of the earth. ELECTRICITY EXCITED BY THE BURNING 448. M. Becqueral has found, as the reof paper is set on fire at one end, the flame sult of numerous experiments, that when a roll thereof becomes negatively electrified, and the paper positively. He also found that when alcohol is burned in a copper dish, the latter becomes positively electrified. HARE'S SINGLE GOLD-LEAF ELECTROMETER. 449. This instrument consists of a glass vessel, fixed by a foot to a wooden stand, and having an aperture at the top, and also another at one side. The top is closed by a metal cap, finished externally by a horizontal zinc disc, six inches in diameter, and connected internally with a single leaf of gold, cut into an acute triangular form, and hanging on the centre of the instrument, with the point downwards. Opposite to the lower end of this leaf of gold, is a ball attached to a horizontal wire, and which, passing through a screw cap fixed in the lateral opening of the glass vessel, can be made to approach to, or recede from, the leaf at pleasure, the distance being estimated by a graduation of the screw into of an inch. A plate of copper, six inches in diameter, and furnished with a glass handle, generally accompanies the instrument. of 450. The electricity produced by the contact copper and zinc, is rendered sensible in the following manner :-Place the disc of copper on the disc of zinc; take the micrometer screw in one hand, touch the copper disc with the other, and then lift this disc from the zinc. As soon as the separation is effected, the gold leaf will strike the ball, usually if the one be not more than of an inch apart from the other. That the phenomenon arises from the dissimilarity of the metals, is easily shown by repeating the experiment with a zinc disc, in lieu of a disc of copper. The separation of the homogeneous discs will not be found to produce any contact between the leaf and the ball.' 451. It is probable that the sensibility of this instrument is dependent on that property of electricity which causes any surcharge of it, which may be created in a conducting surface, to seek an exit at the most projecting termination or point connected with the surface;' this disposition being increased, of course, by the proximity of the ball. These effects are not to be expected in weather unfavorable to electricity; but in favorable circumstances they have been produced by a smaller instrument, the discs being only two inches and a half in diameter. PYRO-ELECTRICITY OF MINERALS. 452. M. L'Abbé Haüy has remarked, with regard to the electricity produced in certain crystals by an alteration of temperature, that it is of two kinds. The accidental circumstances which led to the discovery took place whilst he was examining some crystals of the oxide of zinc, from Limbourg, near Aix-la-Chapelle, and fragments of the acicular variety of the same mineral from Brisgau. Having placed a piece of one of these substances in a very cold window for a few moments, it was found, on examination, to be electrical. Its poles were ascertained, and the mineral then placed in a milder temperature, when the electricity soon become null; but, being approached to a fire-place, the power was greatly renewed, but the poles were inverted. 453. These results have been verified by M. Hauy on other crystals, especially those of the tourmaline. In taking them for examples, he has endeavoured to bring under one point of view all that passes with respect to them in the interval comprised between the limits of temperature, beyond which the electric action disappears without return. He has given the name of ordinary electricity to that produced by heat, and extraordinary electricity to that produced by cold. If, therefore, commencing at the point where the excess of heat destroys in the tour maline the effects of the ordinary electricity, that mineral be left to cool, it will soon give signs of ordinary electricity. The action of the poles at first feebly augments to a certain degree, beyond which it gradually diminishes, and at last disappears. With a temperature a little lower, however, the extraordinary electricity appears, and the poles resume their power, but in an inverted order, so that the pole at first positively electrified becomes negative, and the negative pole becomes positive. ELECTRICITY OF THE ATMOSPHERE. 454. M. Bourdet, an ex-captain in the French service, has described in a letter, a very singular electric phenomenon which he witnessed in Poland, December 24th, 1826. The weather, according to the Poles, had never been milder at that season of the year, no snow had been seen, nor had the usual cold weather of the north, which generally set in early in that country, then commenced. Rains and storms, however, were frequent. I was,' says M. Bourdet, with the advanced guard of light cavalry; the commander gave me an order to halt in the rear and see that my guns were disembarrassed, and then to rejoin, as quickly as possible, the light brigade. In spite of the efforts of my mer, the guns were not cleared from the marshy ground in which they were entangled, without great labor. We were advancing across the field about nine o'clock in the evening, when a strong gust of wind suddenly arose, the sun had shone brightly during the day, and, in a few minutes after, the night became so dark that we could not see the heads of our horses. The wind blew so violently that the horses stopped. At that moment the extremity of the hair on their ears became luminous, as well as all the longer hairs on their bodies except the locks on their manes and tails. All the metallic extremities of their harness, and all the metallic sharp points of the carriages of our guns, were studded with luminous points, so that one might have supposed, had it been spring, that a swarm of glow-worms had covered our horses and guns. Our quarter-master observed that the points of my mustachios were luminous. The same phenomenon was seen on some of the cannoneers, but none of us had our eye-lashes or hair rendered luminous. These lights remained as long as the gust of wind lasted, namely, for three or four minutes. Their color was a soft violet, and they terminated in a bright white. The horses held their heads high, their ears were erect and moving, their nostrils open and respiring, their manes and tails erected, their fore legs thrown forward and their hind ones back. Their attitude, in general, was that of animals seized with terror. During the time the wind blew, they remained at a full stop, and, when feeling the spur, some stood stock still, and others kicked, as if they had been reluctant to advance. When the wind ceased the lights disappeared, and a deluge of rain, mingled with hail, fell. But, though the obscurity continued, our horses moved on, shaking themselves at times, panting forcibly, and neighing; but they continued on their march. On arriving at the advanced post, I mentioned to my comrades the phenomenon we had witnessed, and though they had been only three leagues from us, they felt no wind, but experienced much rain. The wind we encountered had an opposite direction to the rain. RELATION OF A REMARKABLE ELECTRICAL PHENOMENON. 455. The following relation is made by M. Allemand, of Fleuvier Neufchatel, to M. Pictet, and is published in the Bib. Univer. M. Allemand, states that on the 3d of May, about ten o'clock in the evening was caught in a violent storm of wind and rain. The thunder becoming frequent and strong, he thought it proper to close an umbrella he had with him, and hold the upper metallic point in his hand, lest it should attract the lightning. The night, dark of itself, was made more so by the great rain. Suddenly he perceived a light from above, and looking upwards found the edge of his hat luminous. Supposing at the moment the hat was on fire, he, without reflection, passed his hand over the light to extinguish it. It, however, only shone more strongly, a circumstance which caused some confused ideas on the nature of the light. The hand being filled with water from the hat, on shaking it, M. Allemand saw that the interior of it shone as if it were a polished metal reflecting a strong light. 456. Being at this time near the farm of Chaux, about ten or twelve minutes' walk from Fleurin, and fifteen or twenty from Motiers, M. Allemand considered for a moment what he had best do, and concluded on continuing his progress. Having once filled his hand with the electrified water with impunity, he ventured to repeat the experiment, and did it fifteen or twenty times, endeavouring to ascertain whether it had odor, or produced any decrepitation or sound; but nothing of this kind could be perceived; nothing but the bright light, which seemed like a brilliant varnish on the hand. The light remained for an instant only. At a few hundred paces farther on, the light on the hat still continuing, M. Allemand was surprised by the appearance of another light, less bright than the former, on the smooth surface of the umbrella handle, at the place where generally a plate of metal is placed for the name, but which plate had been removed from this umbrella. At first the finger was passed over it to extinguish it, but the phenomena were just as before, and ACCUMULATION of electricity, 118. both the rubbing and rubbed surface shone brightly. Afraid of the metal about the umbrella, it was thrown down, and M. Allemand went on his way, rubbing his hat on the sleeve of his coat; but in this way only rendering the light brighter. The thunder was more frequent than before, but still at some little distance. The crown of light continued until M. Allemand arrived near Motiers, and he attributed its cessation to the high poplar trees in the neighbourhood of that place. Stopping at Motiers only a short time, he took a guide with a lantern to find the umbrella. Having done so he sent back As the tempest had diminished, he used the umthe man, and went on himself towards Fleurin. brella; and, as soon as the light of the lantern was sufficiently removed, he again remarked luminous appearances. These occurred at each end of the whalebone ribs, on the metal point which terminates them: the light was not so bright as the electric star, but they were brilliant points like a yellow red metal, highly polished, and would, M. A. remarks, have appeared very beautiful if he had been collected enough to admire them. M. Allemand explains these effects by supposing the atmosphere sursaturated with electricity, and that a portion of it was continually passing to the ground, through his hat, umbrella, and himself. ILLUMINATION BY ELECTRICITY. 457. Professor Meinecke of Halle, has, in a late number of Gilbert's Annals, proposed to illuminate halls, houses, and streets, by the electric spark, and expresses his strong persuasion that one day it will afford a more perfect and less expensive light than gas-illumination, and ultimately replace it. His plan is to arrange, what are called in electricity, luminous tubes, glasses, &c., i. e. insulating substances, having a series of metallic spangles at small distances from each other, along the place to be illuminated; and then by a machine send a current of electricity through them: sometimes also partially exhausted glasses, as the luininous receiver, conductor, &c., are used. In this way professor Meinicke obtained from a two feet plate machine a constant light in his apartment, equal to that of the moon, and even surpassing it; and by enclosing his system of sparks in tubes filled with rarefied hydrogen gas, in which gas it is assumed that the electric spark is more than doubled in brilliancy, thinks it will be easy to enlarge the plan to any extent. INDE X. AGENCY of electricity in various luminous phenomena, 278. AMBER, its electrical properties, 2. ATMOSPHERICAL ELECTRICITY, 272. ATTRACTION attendant on excitation, 43. ATTRACTION and repulsion, 96. BENNET, Rev. Mr., his electrometer, 153. His doubler of electricity, 186 |