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PROFESSOR CUMMING's TABLE OF THERMO concludes that it is owing to the superior conELECTRICS.

ducting property of that fuid. The degree of 616. In the following table of thermo-elec- ignition, all circumstances being the same, will trics, by professor Cumming, each substance is correspond with the .elations in which the mepositive to all below, and negative to all above dium containing the wire stands to conduction. it, two being used together.

626. Platinum and steel wires may be ignited

in carbonic acid gas, hydrogene, cyanogene, and Bismuth, Cobalt, Brass, Charcoal,

olefiant gas. Alercury, Silver, Copper, Plumbago, Nickel, Tin,

627. Gold wire was wrapped round platinum Gold, Iron,

in all its extent; and this double wire placed as Platina, Lead, Zinc, Arsenic,

the uniting wire between the conducting rods Palladium, Rhodium,

Antimony

It was ignited throughout, and the fusion of the ANALOGY BETWEEN THE PHENOMENA OF Gal- into little spheres of a prolate form, at equal

gold wire supervened, the gold being collected VANISM AND THOSE OF FERMENTATION.

distances, and appearing like a row of beads. 617. M. Schweigger has observed this analogy 628. Steel wire was, in like manner, entwined in the following points :

with gold wire. It also was ignited in its whole 618. (1.) Galvanic piles, like fermentable extent; the gold wire was fused, and exhibited mixtures, exhibit their effects only by the reci- the bead-like form. procal action of three different bodies.

629. Platinum was woven with copper wire. 619. (2.) The products of galvanic action are The platinum wire was ignited throughout; the two, an oxidated body, and a hydrogenated body. copper wire not undergoing fusion nor The same happens with the products of fermen- ignition. tation, which are alcohol and carbonic acid.

630. It may here be remarked, that, in the 620. (3.) The presence of electro-negative ignition and combustion of steel wire, for inbodies favors the decomposition of water, whilst, stance, the fusion is primarily confined to the suraccording to Dobino, a similar effect goes on in face, and the fused scale or film may, perhaps, fermentation.

not penetrate more than one-third the diameter ExperIMENTS ON THE IGNITION OF WIRE.

of the wire, while the remaining part may not

have undergone the least physical change. The 621. The following experiments on the igni- fused matter formed itself into spherules, with tion of wires are very interesting. Being con- regular intervals. This appears to be a curious nected with the phenomena of caloric developed phenomenon; and it will also be observed that, in the action of the galvanic battery, they may be when the calorific heat is short of ignition, the acceptable as a contribution towards that mass steel wire will be blued in patches. of facts which will at some future period assume 631. Steel wire was doubled for one-half its a more scientific form.

extent; the single and denuded part was alone 622. In these experiments, Mr. Murray used ignited. four porcelain troughs, each containing ten cells, 632. Platinum wire was doubled for one-half and each cell supplied with one and a half its extent; and that part only which was single Auid ounce of the strongest nitrous acid, being could be ignited. filled up with water to the depth of two-thirds, 633. Steel wire was partly enveloped in gold and properly mixed with a glass rod. Nitrous wire; only that portion of the steel wire which acid, in this proportion, he has ever found best was void of the gold wire could be ignited; the calculated for the development of galvanic ac- part encased in the folds of the gold wire was tion. Fifteen to eighteen inches of fine platinum partially blued, and was rendered magnetic. wire may be readily ignited. He of course used 634. Copper wire was twisted round platinum the triad (four inches square), for which we are wire, for half the length of the latter. The unindebted to the sagacity of that ingenious and covered platinum was alone ignited. Copper wire profound philosopher, Dr Wollaston.

was twisted around steel wire in the manner of 623. When sulphuric acid is employed, as is the preceding; the naked steel wire was ignited done most injudiciously by some, in mixture alone. Steel wire was twisted round platinum with the nitrous acid, the vapor is perfectly in- wire, for one-half its length; only that portion tolerable, and much of the action is no doubt of the platinum wire excepted from the steel lost and expended in vapor, and in the great tem- could be ignited. perature developed at the same time.

635. Peculiar phenomena are connected with 624. In connexion with the subsequent detail, these exhibitions. When the second wire is

be

proper to mention, that a riband of a carried through the whole extent of the uniting platinum foil, was suspended from one of the con- wire, ignition is superinduced throughout; but ductors, and brought in contact with the mer- when only partial, the ignition is confined to the curial surface (that metal being contained in a denuded portion. shallow glass-basin), while the other one is 636. Copper, platinum, and copper wires, plunged into the mercury, deflagrates with great were linked together, and made the communibrilliancy, and oscillates like a pendulum. cating chain. The platinum placed between

625. We may now state generally, that steel the copper wires was ignited alone. and platinum wires may be intensely ignited, in 637. Platinum, copper, and platinum wires, alcohol, ether, and its vapor, oil of olives, naph- exhibited, on the tract of either platinum wire, tha, and sulphuret of carbon. Mr. Murray has ignition, while the intermediate copper wire renot succeeded in igniting these in water, and mained dark and unignited.

it may

638. In the case of steel, copper, and steel munication with the discs. When the brass cap wires (so linked together), the steel wire on each is in its place, the columns descend vertically, side was ignited, while the copper wire remained and the lower ring is one-fourth of an inch disunaltered.

tant from the bottom of the glass. The axes of 639. In the chain of platinum, steel, and pla- the columns are one inch and seven lines distinum wires, the platinum wires were exclusively tant, but may be brought nearer one another. ignited, and the steel unignited.

From the centre of the cap rises a tube of glass, 640. In that of steel, platinum, and steel, the varnished within and without, and within the intermediate link of platinum was ignited, and tube is a brass wire kept in the axis by a cork, the steel wire on each end remained without but touching the tube no where else. At the ignition.

lower end of the brass wire is suspended a piece 641. In a chain of gold, steel, and gold, the of gold leaf, two inches and a half long and gold wires on each end were ignited and fused, three lines wide, exactiy in the middle of the and the intermediate steel was not ignited. interval between the two columns, and parallel

642. In one formed of steel, gold, and steel to their axis, if they are accurately vertical. At wires, the central one of gold was exclusively the upper end of the brass wire is a small brass ignited.

ball, upon which may be screwed one of the discs 643. Mr. Murray next tried spiral coils of of a condenser, as in the electrometer of Volta. platinum and steel, of various diameters, and By this arrangement, the electrical columns found that they were ignited, though curvilinear, which Behrens had placed without the glass, in the same manner as if the wires were not which defends the gold leaf from the agitations curved.

of the air, are placed within the glass, so that 614. The preceding experiments seem to their position is not only better preserved, but prore, that the caloric developed in galvanic they are defended so completely from mois. action, has no relation with the medium in ture, dust, &c., that they retain the same eler which the ignition takes place; and that it is trical intensity. evolved in some inverse ratio of the conducting 648. This electrometer is used in the following properties of the uniting wire.

manner :—The cap of metal is put in commu 645. The phenomena of ignition in links of nication with the ground by means of a metallic various metals united into chain, seem con- wire, and by touching the brass ball, any accinected with the passage of a material agent dental electricity is discharged, which may be through them, displaying its powers in greater long to this part of the apparatus. If the skin or less ignition, according as the passage is in- is dry, the touch of the finger is not suffi terrupted, or its fire more or less retarded, and, cient. As the gold leaf is suspended between of course, as the amount of the resistance. the columns, at the level of the rings of metal The agent or agents, therefore, developed in which terminate them, the one positively and transitu from pole to pole, will swell into igni- the other negatively, the gold leaf is attracted tion, if the conducting power of the medium equally on both sides, and remains quietly in traversed is low, or even burst its metalline con- the middle in its ordinary state; but if, by fine, and expend its impetus in all the brilliancy means of the metallic wire, we communicate to of an intense combustion. The gold, platinum, it the weakest degree of electricity, the lower and copper wires, were path of an inch in dia- extremity of the gold leaf is attracted by the meter; and the steel the finest harpsichord wire. ring which possesses an electricity opposite to DESCRIPTION AND USE OF A VERY SENSIBLE tact with this ring, it is successively repelled and

that which is communicated. Having come in conELECTROMETER, FOR INDICATING THE KIND attracted by the opposite ring. This oscillatory OF ELECTRICITY WHICH IS APPLIED TO IT.

motion continues till the gold leaf attaches itself 646. Some years back, M. Behrens published to one of the columns, from which it may be easily the Description of an Electrometer, which in- detached by touching the brass wire, so as to disa dicates the kind of electricity that is presented sipate its electricity, and by shaking the instruto it; but it appears to have been forgotten, with ment. In order to determine the nature of the the dry electrical columns, which formed an es- electricity, the upper poles of the two columns sent al part of the apparatus. The electrical which project above the brass cap have the signs perpetual motion of Zamboni is similar to this + and upon them, and the electricity reelectrometer, and M. Butzengeiger was employed quired is that which is indicated by the sign of to execute one of them, which we may proceed the column towards which the gold leaf first to describe.

moves, or which it first touches, when the elec647. A cylindrical vessel of glass about two tricity is stronger. inches and a half in diảmeter, and three and a 649. By this electrometer, strong and weak half high, has fitted to it a brass cap, from which degrees of electricity may be equally well extwo small dry electrical columns descend into amined. In the first case, the electrified body the vessel, and are attached to the cap by screws, is made to approach slowly and at a distance so that the one has its positive and the other its the ball of the electrometer, till the gold leaf is negative pole, making a slight projection above put in motion towards one of the columns. If, the cap. Each column is composed of 400 for example, we bring an excited stick of dises of gold and silver paper, glued together, sealing-wax to the distance of about three feet and three lines in diameter, so as to fill two from the ball, we shall observe a motion of the tubes of varnished glass. Each of these tubes gold leaf towards the column marked It s terminated below by a ring of brass, projecting a we bring it to a less distance, it will strike the litle, and rounded, which is in electrical com- column, from which it may be easily detached,

by bringing the wax still nearer. In the second is a piece of card-board, on which circles are case,

the electrified body must be moved much marked and divided, indicating the number of nearer the ball, and brought into contact with degrees through which the needle may have it, if necessary, till the gold leaf is put in action. moved. This degree of electricity is so weak, that it 654. The conductor, whose state was to be would be absolutely insensible in the ordinary indicated by this needle, was sometimes a band electrometer of Bennet.

of tin 0:4 of an inch broad, and 24 inches long; 650. When the electricity is still feebler, we sometimes a brass-wire belix, which, being may advantageously employ a condenser adapted brought up close beneath the needle, formed a to the instrument. The circular plate, on the kind of condenser, and rendered the action more margin of which is screwed the ball of the elec- sensible. trometer, replaces the cover of the condenser, 655. (1.) The tin band was placed under the and a plate of disc furnished with a glass needle, both being parallel to the magnetic mehandle, and which is placed above the first, re- ridian; a small glass was filled with muriatic presents the base. These plates are covered acid; the end of the band, towards the austral with a thin coating of amber varnish on the faces pole of the needle, was plunged into the acid, which are brought into contact. If we wish to and, in a few moments after, the other extremity try a very weak electricity, we first touch, in was immersed; immediately the austral pole order to deprive it of its electricity, the inferior went to the east. The experiment being replate, or the wire which carries the ball; we peated, except that the end of the band, corthen place above it the other plate, and afterwards responding to the boreal of the needle, was first touch the lower plate or its wire, with the body immersed; the austral pole went to the west. whose electricity we wish to examine, touchiny When, in place of muriatic acid, a solution of at the same time, the upper plate, in order to ammonia, mineral alkali (soda), or sal-ammonia, deprive it of its electricity. The upper disc is was used, the results were exactly the same; but then removed by its glass handle, and we observe ifa solution of vegetable alkali (potassa) was used, towards which of the two small columns the gold the deviations were all in the opposite directions. leaf is carried, and the sign marked upon this Pure water produced no effect, but sdo of acid column will indicate the kind of electricity. If, made it active. All solutions of salts, or acid, for example, we put in contact with the lower thus applied, produced an effect upon the needle. surface of the lower plate of the condenser a It appears in these cases that, according as the small disc of zinc, about three-fourths of an first contact is made to the right or left, an arinch in diameter, and press it against this plate, rangement of molecules is established in the fuid, without touching the plate with the finger, and proper to form a species of pile of which the if we touch at the same time the upper disc of two poles are very distinct, and that the whole the condenser, to deprive it of its electricity, of this little pile is reconstructed in the opposite and if we afterwards remove the disc of zinc direction, when the contact is made in the oppoon one side, and on the other side the

upper

site way. plate, we shall observe the gold leaf approach 656. Place the needle over the condenser, the the column marked minus. A similar effect will wires of the latter and the needle being parallel be observed, if we put in contact with the disc to the magnetic meridian; hold a cylinder of zinc of the apparatus the metallic side of a piece of in perfect contact with each end of the wire of silvered paper.

the condenser, the arrangement will then be zinc, 651. It will often be more convenient to put brass, zinc; plunge the cylinder corresponding the body we wish to examine in contact with with the austral pole of the needle into muriatic the upper and moveable plate, and touching acid, and then plunge the other into the same the inferior plate, to deprive it of its electricity, acid, the austral pole of the needle will go toproceding in other respects as we have already wards the east. "Repeat the experiment with described. The electricity, however, which the nitric acid and fresh cylinders of zinc; now the instrument now indicates, will be opposite to austral pole of the needle will go towards the that which is communicated to the upper plate, west. These and other results are the same, because, by this method, the plate united to the whether the conductors are put in contact with instrument forms the base of the condenser. the metals before or after their immersion in the

652. If the body which we examine cannot fluid. be conveniently put in immediate contact with 657. The needle condenser and metal bars the lower plate of the condenser, a communica- (zinc), being as before, let the glass be filled with tion with it may be formed, by means of a me a solution of potassa, then immerse the end of the tallic wire, with an insulating handle, the rest of bar corresponding to the austral pole of the the operation being the same as before.

needle, and afterwards the other bar; the austral ELECTRO-MAGNETIC EFFECTS

pole will deviate to the east. Take the bars out

of Alkalies, of the solution, but without changing their posiACIDS, AND SALTS, BY M. YELIN.

tion in the hands, and, as soon as the needle is 653. The magnetic needle used by M. Yelin at rest, introduce them again, beginning with was nearly 1.5 inch long, and .008 of an inch the bar corresponding to the boreal pole of the in diameter. It weighed little more than half a needle; the needle (the austral pole) will now grain, and was delicately suspended by a spider's deviate to the west. Take the bars out of the web, from a rod passing through the top of a fluid, and, without changing them from hand to glass cylinder, so that it could be raised or low- hand, turn them so that the ends which were before ered at pleasure. The bottom of the instrument immersed in the liquid, shall now be in contact

with the extremities of the condenser wire, then elements of a species of pile, of which the extre repeat the above experiments, and the same re muities may be detached without losing their elecsults will be obtained. Finally, if the bars, tricity; and, in consequence of this property, I being well cleaned, are changed from hand to call it a secondary pile, with mobile unipolar hand, and the experiments again repeated, the extremities. same results will be produced.

664. “I have sometimes succeeded, with bars 658. But now, preserving the apparatus as it of some length, in obtaining distinct poles at each was, change the solution of potassa for very pure extremity, so that when the bars were turned, muriatic acid. The zinc bar, corresponding to opposite results were presented by the needle; the boreal pole, being first immersed in the acid, but I have not been able to discover the condition the austral pole will go eastward. Remove that of this phenomenon, so as to be able to produce har from the acid which was last plunged in, and it at pleasure.'. a little while after, the other bar, and without 665. M. Yelin remarks, however, that he has changing them at all in the hand, wait till the never yet been able to ascertain the existence of sieedle is quiet; commence by the bar corre- free magnetism, or electricity, in any of these sponding to the boreal pole; at the moment bars. Many other experiments are given in when that which agrees with the austral pole tables, which we have not room to notice, though shall touch the acid, the needle (the austral pole) they are of great interest. The bars M. Yelin will deviate towards the west, and it will go in used were .275 of an inch in diameter, and 2:75 the same direction as ofien as the experiment is inches long.— Bib. Univ. xxiii. 38. repeated, whether the operation be begun on the right or on the left hand.

TERRESTRIAL MAGNETISM. 659. If the bars be then well washed and 666. The following curious electro-magnetic dried, and restored to the ends of the condenser experiment was exhibited by Dr. Birkbeck, at wire they were in contact with before, but with the London Institution. A hollow globe of wood, that part which was before immersed, now in fifteen inches in diameter, was first accurately contact with the wire, and the immersions and turned, and, from the equator towards each exexperiment be repeated, one of these two things tremity of its axis, grooves were cut parallel to will happen : either the needle will constantly the equator, at the distance of 4jo from each move to the east, whichever bar is first immersed, other, like parallels of latitude, and another, or the action will be very doubtful or null. rather deeper, groove from one pole to the other,

660. If, instead of turning the bars, they are along a meridian half-round. changed one for the other, the needle will go 667. Beginning now at the equator with the constantly to the west, whichever bar is first middle of a wire, about ninety feet in tength, immersed; but the previous results may be at and one-tenth of an inch in diameter, which just any time restored by re-changing the bars, and fitted the grooves, it was carried round in the then the needle will go to the east.

successive circles towards each pole, making an 661. The faculty thus acquired by the bars of abrupt turn from one circle to another along the zinc, of becoming positive or negative, accord- meridian groove above-mentioned. From the ing as they are plunged either first or last in the point where the wire arrived at the poles, it was acid, they preserve some time. They may be carefully bound with silk, and returned back washed, dried, and held in the hand, without again to the equator along the same meridian. losing their state, and hence particular precau- The two ends of the wire being thus brought tions are required in making delicate experi- together, they proceeded to a little distance from ments with the metals.

the globe, where they terminated. By this means 662. This faculty is not communicated either the effect of the short abrupt turnings of the wire to the fluid or to the extremities of the condenser along the meridian towards the poles, is counwire

. All the metals which become magnetome- teracted by wire returņing back again from the ters by muriatic acid, as well as all the acids poles to the equator, leaving thereby only the which produce an electro-magnetic action with parallel wires active when the two extremities homogeneous metals, produce the same pheno- are connected with the battery.

668. The globe being thus far formed, it is 663. These experiments may be compared, covered with zones, in the usual way, so as to with interest, with the observations of M. Volta, exhibit to appearance a common fifteen-inch terthat a band of wet paper, making part of the restrial globe, the wire being completely hidden. conductor of his pile, becomes charged with But this covering is so laid on that, instead of electricities, which it preserves some time; with the terrestrial pole coinciding with the poles that of M. Gautheret, who thought he remarked formed by the wire, the latter is brought into lat. something similar in the conducting wires of the 75° N., and long. 76° 40'W., which is the situpile; and with that of M. Ritter on his secondary ation which Mr. Barlow conceives will best agree piles, the phenomena of which M. Volta attribu- with the observed bearings of the needle in most ted to the electro-motive action of the alkalies parts of the world. Things being thus adjusted, and salts interposed. “A very decided electric the globe is placed on a large cup near the batcharge may be remarked in the metals interposed tery, so as to admit of its being placed in any between the conductor and the fluid; they are position, or so as to bring any part to the zenith, both unipolar, i. e. charged each with a single without the encumbrance of the usual brazen electricity, which (ney retain for some time, and meridian and horizon. A needle is now susthis electricity is constantly positive in one, and pended over the globe, leaving it free to take any Degative in the other. They form, therefore, the dip; while, by means of a silk suspension, it is

mena,

also free to take any direction; lastly, the needle as may be ascertained by determining the angle is insulated from the action of terrestrial mag- which the needle makes with the magnetic merinetism, by opposing to it the north end of a small dian, after it has assumed a fixed position, by bar magnet in the line of the dip. By this means means of a divided circle adapted to the case the needle retains its magnetic power, but is which covers it. A simple conducting needle, under no magnetic influence.

suspended by a metallic wire of proper diameter 669. The extremities of the curves being now and length, might be substituted for the magnetic connected with the poles of the battery, the one; but M. Rousseau's apparatus is much more globe immediately becomes strongly active upon convenient, and sufficiently sensible for the kind the needle, causing it to assume the same dip, of effect which it is his object to measure. and the same direction, with respect to the arti 672. To use it for ascertaining different deficial globe, as the actual needle does in the grees of conducting power, it is sufficient to corresponding part of the earth itself, at least to place the substance submitted to experiment in a very considerable extent. Thus, if we bring the electrical current, taking care that the thickthe Island of Ascension to the zenith, the needle ness which the electricity has to pass through be is found perfeetly horizontal, with a slight wes- always equal. If the fow of the quantity of terly variation. If we bring London to the electricity necessary to produce the greatest dezenith, we find the dip about 70°, and 24° or 25° viation be not instantaneous, the time required of westerly variation; if the globe is again by the needle to assume its fixed position may shifted in position, so as to bring Cape Horn in be taken as the measure of the degree of the conthe zenith, the dip is about 60° the contrary way, ducting power of the substance employed. that is, with the south end below; and the 673. To submit liquids to this kind of examivariation about 30° easterly, and so on with nation, M. Rousseau places them in small mevarious other places.

tallic cups, communicating by their foot with 670. The purpose of this experiment is to the needle and the ball: he then places in the show, that what we have hitherto considered as liquid one of the extremities of the metallic wire, the magnetism of the earth, may be only modi- covered with gum lac, that the same surface of fied electricity, and to illustrate, experimentally, metal may always be in contact with the fluid, the theory advanced by M. Ampère, who attri- and measures the duration of the needle's motion butes all magnetic phenomena to electrical from the moment when the communication is results.

established with the pile by the other extremity RoUssEAU'S APPARATUS.

of the wire.

674. By submitting the fixed vegetable oils 671. M. Rousseau, who has been occupied employed in the arts and in domestic economy several years in the construction of dry Voltaic to this kind of proof, M. Rousseau has estabpiles, has conceived the idea of employing those lished a very singular fact, which may be useful instruments to appreciate the different degrees in commerce; it is, that olive oil possesses a very of conducting power of the substances arranged inferior degree of conducting power to that of in the class of bad conductors of electricity. For all other vegetable or animal oils, which neverthis

purpose he has contrived the apparatus wetheless present, in all their physical properties, are about to describe. The dry pile, which forms the strongest analogies to that substance. For the principal part of it, is made of discs of zinc instance, every thing being equal in both cases, and tin-foil, separated by pieces of parchment, olive oil required forty minutes to produce a soaked in a mixture of equal parts of oil of pop- certain deviation, while poppy oil, or the oil of the pies and essence of turpentine; the whole is beech-mast, required only twenty-seven seconds covered laterally with resin, to prevent the con to produce the same deviation. One-hundreth tact of the air. The base of the pile communi- part of any other oil added to oil of olives recates with the ground. Its upper extremity may duces the time to ten minutes. It would, therebe connected by a metall:c wire with an insu- fore, be easy to discover, by means of this instrulated vertical pivot, carrying a weakly magnetic ment, the smallest traces of any oil fraudulently needle, balanced horizontally. On a level with mixed with oil of olives. the needle, and distant from the pivoi, about 675. If the proportion of the foreign substance half the length of the latter, is a metallic ball, be considerable, the difference of time necessary also insulated, but communicating with the pile. to produce the maximum of effect would no It is evident that, by this arrangement, the elec- longer be sufficiently great, and could not be tricity accumulated at the upper pole of the pile measured with sufficient precision to indicate the is communicated to the needle and the ball; and proportion of the elements, but the apparatus consequently repulsion ensues, tending to sepa- might easily be modified so as to adapt it to this rate the needle, which is moveable, from the ball kind of determination. which is stationary. If we place the pivot and 676. The solid fats are worse conductors than the ball in the magnetic meridian, the needle the animal oils, arising, no doubt, from the large touches it, and remains at rest as long as the ap- proportion of stearine contained in the former ; paratus is not connected with the pile; but the for M. Rousseau is satisfied, by comparative instant the communication is established between trials with stearine and elaine, prepared by M. them, the needle is repelled; and, after some os- Chevreul, that the conducting power of the latter cillations, takes its position of equilibrium, de- much exceeds that of the former. The fat of an pending on its magnetic power and the energy of animal becomes a worse conductor in proportion the pile. These two quantities remain constant to the age of the individual which affords it. for a considerable time, with the same apparatus, 677. By means of the same apparatus, we

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