« PreviousContinue »
to intensity, simply on account of its brevity, and application of the electricity so conveyed, to proits convenience in forming a double noun with duce at the distant station some striking phenomelectricity. Electricity of intensity then, or ten- enon, which, according to a preconcerted arrangesion-electricity, is electricity characterized by the ment, shall represent a letter of the alphabet, a greatness of its intensity—or whose intensity is numeral, a word, a sentence, a paragraph, or the greater than its quantity. Electricity of quantity, like. A source or fountain of electricity, conon the other hand, has its quantity greater than ductors to carry it, and a dial plate on which it its intensity The intensity diminishes as the shall cause an index to exhibit signals, are thus quantity increases ; but the ratio which the one the essential elements of an electric telegraph. bears to the other differs through a very wide Our present object is to discuss chiefly what is scale, so that a knowledge of the degree of the electrical in the telegraph—without much refone does not often enable us to predicate the erence to the mechanical devices or subsidiary amount of the other. Practically, we have no arrangements which it involves. Our first condifficulty in reducing both to a minimum, or in cern, then, is with the source of electricity ; and, exalting the one whilst we reduce the other ; but as our space is limited, we shall confine ourselves we cannot at once exalt both intensity and quan- to the voltaic battery, the apparatus chiefly in use tity. The discovery of a method of effecting this along the telegraph lines. A voltaic battery, in will make a new era in the science; and admit its simplest form, consists of two dissimil solids of the most important applications to the useful -generally metals—arranged side by side, witharts. Meanwhile we may compare electricity of out touching each other, in a liquid which distension, as we have done already, to high-pressure solves only one of them. One of the solids is steam issuing in small jets under great pressure ; almost invariably a plate of zinc, rubbed over and electricity of quantity to the thousands of cubic with quicksilver, or, as it is called, amalgamated. feet of invisible vapor which arise softly every The other is copper, iron, silver, gold, or platimoment from the surface of the sea. Or the num ; the last being preferred for very powerful former may be likened to a brawling, gushing batteries, and admitting of being replaced by coke. mountain brook, rushing with great force but lit- For telegraph-batteries, amalgamated zinc and tle volume of water; and the latter to the slow copper, or zinc and silver, are generally employed ; rolling Amazon or Mississippi, silently moving and the liquid in which they are dipped is diluted onwards to the sea. Or the first to a swift, sud- sulphuric acid — which dissolves the zinc, but does den hailstorm or avalanche, and the second to the not affect the copper or silver.
Let us suppose inexhaustible glacier, constantly melting, but as copper and zinc to be the metals selected. We constantly increasing. Or the one to an instan- have it in our power to take all the copper we taneous gust or white squall, passing off in a propose to employ, in one large sheet, and all the moment, and the other to the unceasing trade zinc in another; or we may cut down each sheet wind, forever sweeping gently over the bosom of into many small ones. The quantity of electricity the waters.
evolved by a voltaic battery is chiefly determined It depends upon the purpose to which electricity by the size of the plates made use of; but if we is to be applied, whether it should be chosen take a single sheet of zinc, however large, and a great in quantity, or great in intensity. If the single sheet of copper, we find the intensity of the chemist desires to analyze a gaseous mixture by electricity they evolve exceedingly feeble. detonation, he will use the friction-machine, to the other hand, we cut down each of the large supply a momentary spark of great intensity. plates into several smaller ones, and arrange these But the electro-plater, who has constantly to de- so that the copper and zinc shall be placed compose a compound of gold or silver, employs alternately, in a way to be presently described, the magneto-electric machine, or a small voltaic we find the quantity of the electricity much diminbattery—which furnishes great quantities of elec- ished, but its intensity greatly increased. Unless tricity of considerable intensity. The electric the intensity be considerable (although it need not light requires both quantity and intensity to be be very great) the electricity cannot force its way very great. For the electric clock the intensity along a great length of conductors; and, if its may be at a minimum, and the quantity need only quantity be not great, its effect will be but mobe moderate. The electric telegraph demands mentary. Plates, however, a few inches square, great quantity, but the intensity need not be very supply a sufficiency of electricity for the longest high.
telegraph line; and from twelve to sixty pairs of This much premised, we may now consider its such plates are as many as are required. The application to the construction of the telegraph. exact number needed will be determined by the An electric telegraph consists essentially of three distance which the electricity is to travel. By things. First, a voltaic battery or other appara- varying the number and size of the plates, as well tus to evolve, when required, electricity. Sec- as the strength of the acid in which they are ondly, an arrangement of metallic wires or other dipped, the quantity and intensity of the electricgood conductors, to convey the electricity to the ity may be modified through very wide limits. distant places with which telegraphic communi- A voltaic battery, strictly speaking, consists of cation is to be carried on, and to bring it back to associated pairs of dissimilar solids, such as zinc the machine from which it set off. Thirdly, the and copper. A single pair, or simple voltaic cir
cle, like a single cannon in an artillery battery, is , was very short ; and it is quite within possibility but an elementary portion of a voltaic battery, that a single voltaic pair of strongly contrasted · which is constructed by arranging several pairs solids, immersed in a rapid solvent of one of them, together. The simplest voltaic battery, then, will will yet be found sufficient for working the longest consist of at least two pairs, i. e. of four plates, existing or conceivable telegraph line. As it is, two of zinc and two of copper. In arranging the intermediate pairs of the voltaic batteries in these, two glass beakers or drinking tumblers are actual use are introduced only to give the requisite taken, and placed side by side, half full of diluted intensity to the electricity generated. They may sulphuric acid. A wire is then soldered to one be ignored in our further discussion ; and our telof the zinc plates, and a corresponding wire to one egraph-battery will resolve itself into a piece of of the copper plates, and one of these plates is copper and a piece of zinc, immersed, without placed in each of the tumblers. The second zinc touching each other, in the same vessel of acidplate is thereafter soldered by one edge to the seculated water. ond copper plate, so as to form one continuous sur- For the sake of simplicity and clearness in our face of metal. The compound plate thus produced further description, we shall suppose the battery is then bent over, so that the soldered edges form described, as locally situated in London ; and that the suminit of an arch, which resembles a saddle, our object is to send messages to Edinburgh, withwith one flap consisting of copper and the other of out communicating with any intermediate place. zinc. This metallic saddle is placed astride of the An iron wire, plated with zinc to keep it from approximated edges of the tumblers, so that the rusting, is connected with the copper plate of the zinc flap dips into the vessel in which the first battery, and then stretched all the way from copper plate with the wire is immersed, and the London to Edinburgh, along wooden poles, erected copper flap into the tumbler containing the zinc some sixty yards apart. In order that the elecplate with its wire. If we wish to enlarge the tricity, which is to travel along this wire, may not battery, we take additional tumblers, and such go elsewhere than to the northern metropolis, the copper-zinc arches as have been described, connect- zinc is insulated, i. e. prevented from coming in ing the vessels, half filled with dilute acid, by the contact with metallic conductors, moist wood, or metallic bridges which dip on either side into the other surfaces which would transfer the electricity liquid ; taking care, also, that all the zinc semi- along the poles to other wires that are generally circles or saddle-flaps shall be turned in one direc- stretched upon them, or to the earth. The insution, and all the copper ones in the opposite, so lation is effected by passing the wire through rings that zinc and copper succeed each other alternately, or short tubes of glazed porcelain, attached to the from the first tumbler at one end of the range to posts, so that the electricity has no choice but to the last at the other. In actual practice, porce- move along the wire. At Edinburgh the wire is lain, or wooden, or gutta percha cells or troughs placed in connection with the signal apparatus, to are generally substituted for glass vessels, and the be afterwards described ; and then is brought back pieces of zinc and copper are not soldered together, to London through separate porcelain tubes along but only connected by movable wires and binding the poles as before, and finally terminates at the
But these mechanical adjustments are detached zinc plate of the battery. In the arrangeonly for greater economy and convenience ; and ment described, which is the earliest and most the battery remains, in principle, identical with the easily understood form of telegraph, it will be arrangement described.
observed that the zinc and copper plates of the batSuch, then, in its most skeleton and simple form, tery at London are connected by one unbroken is the apparatus which is to furnish the primum metallic wire, which extends to Edinburgh, bends mobile of our telegraph. Although each zinc and back there, and returns to London. copper pair contributes to the power of the bat- The wire, however, does not return to the lattery, the whole electricity generated by it mani- ter city, in order to provide a channel for mesfests itself only at the detached zinc plate at the sages being sent from Edinburgh to London, as one end of the battery, and the detached copper well as from London to Edinburgh. Without plate at the other. A battery thus resembles a this returning double wire, (as we shall call it,) or compass-needle or bar-magnet, which appears to an equivalent arrangement of conductors, it is immanifest its inherent magnetism only at its oppo- possible to telegraph from either town to the other, site poles ; although, in reality, it is magnetic even if it were thought sufficient or desirable to throughout its entire length. In the practical ap- send messages only from one of them. It will plication of such a battery, accordingly, no account appear from this, that there must be something is taken of any portion of it but the terminal zinc peculiar in the way in which electricity travels and copper plates, to each of which a wire is along the telegraph-wire. We have compared it attached. To these plates all the intermediate to the transmission of a fluid ; but the wires canones convey the electricity which they respectively not convey it as pipes do gas or water, otherwise set free ; so that we may, after all, properly enough there would be no occasion for the return-wire. A conceive the battery as consisting of a single plate tube extending from London to Edinburgh, and of zinc and one of copper. Such an embryo bat- filled with air or water, might be employed 10 teltery—or, rather, voltaic pair-might, indeed, be egraph from the metropolis to the northern capused for working the telegraph, where the distance ital, as an air-tube is actually employed at the rail
way tunnels near termini ; and but one tube only to zero-or what we may call the northern magwould be needed, messages were sent only from netism neutralizes the southern magnetism, and all London. It is very different with electricity; it indications of free magnetic force cease. must not only travel to Edinburgh, but it must Electricity exhibits exactly similar phenomena. come back to London-otherwise nothing can be in the very act of becoming free, as when it is recorded at Edinburgh ; so that the communica- evolved from a voltaic battery, it separates into two tion must be as complete between Edinburgh and forces—identical in nature, but opposite in the London, although the latter only is to send mes direction of their manifestation—whose intensities sages, as between London and Edinburgh. and powers are equal, and which, like the north
The explanation of this peculiarity, if we avoid ern and southern magnetisms when they meet, the niceties of electrical theory, may be said to be instead of yielding a double electrical force, neufound in the fact, that no electricity leaves the bat- tralize and annihilate the powers of each other. To tery till its terminal zinc and copper plates are the two electricities the names have been given of connected (after a long délour) by a wire or other positive and negative respectively-an unfortunate electrical conductor. It is not as if one wire were nomenclature, as it almost unavoidably conveys the sufficient at least to carry the electricity from Lon- impression that the one is more positive or potent don to Edinburgh. Our electrical messenger is like than the other ; whereas the negative electricity a government courier--who does not start till he has as positive an existence, and as substantial is satisfied that there are relays of horses to make powers, as the opposite electricity—and neither, certain his homeward, as well as his outward in fact, can be produced without the development journey. If there be not a return-wire, or equiv- of the other. The terms in question, like the older alent arrangement, the electricity never sets off ones, vitreous and resinous, are to be regarded, in from London! or, rather, there is in truth no elec- short, as quite arbitrary, and might be replaced by tricity to set off in any direction, till the zinc and any other words or signs ;—though we leave medcopper at that starting place are connected. Till ical men to explain the account which a wilfully a communication is effected between them, the bat- ambiguous critic has given of their electrical actery is equivalent only to a loaded gun. The com- quirements : viz., that their knowledge of elecpletion of the connection is like the fall of the tricity is chiefly of the negative kind ! trigger which fires the charge. In a moment the The twofold magnetism in a bar-magnet has battery discharges its electricity, which, with in- been likened to a double-headed arrow at rest, conceivable rapidity, passes, by the shortest route pointing in two opposite directions, like a windit can find, from the copper plate at the one end of vane. The two-fold electricity liberated from a the battery, to the zinc plate at the other. No battery may be likened to a similar double-headed shorter route, however, is provided for it than the arrow—not at rest however, but rapidly elongatinsulated wires, so that in the case supposed, ing itself in opposite directions, so as to separate although the plates to be connected are only a few its two heads or points further and further from inches apart, the electricity which leaves one of one another. The one arrow-head represents posithem must travel from London to Edinburgh and tive, the other negative, electricity. Thongh they back again, before it can arrive at the other! Our separate, they are never disunited. At first they newest telegraph, in this respect, is like Noah's move straight away from each other ; but their most ancient one.
went to and fro," paths are equivalent to semicircles of the same and his dove “ returned” to the ark with the olive- radius, and are in the same plane, so that they leaf in her mouth.
ultimately meet—and in the act of meeting, each If we look, however, a little more closely into arrow-head destroys the other, and a harmless nonwhat happens, we shall find something still more electric circle is completed. The Egyptian biecurious than we have yet indicated, in the move- roglyphical serpent, devouring its tail, might be ments of the electricity produced by the battery. accepted as the symbol of the closed electric circuit. We have hitherto represented matters, as if only If we apply what has now been said to the teleone current of electricity swept along the wires ; graph, the necessity for the two wires will appear but, in reality, if we are to speak of currents at in a new light. When the plates of the battery, all, we must acknowledge at all times two, mov- consisting of amalgamated zinc and copper, are ing in opposite directions. Electricity, like mag- merely placed apart from each other in dilute sulnetism, always displays itself as a two-fold force. phuric acid, no change of any kind occurs. But A bar-nagnet, or compass-needle, has magnetism if they are connected, as by attaching the zinc to at each pole or extremity. The magnetism of its the one end of the double telegraph wire, and the north pole has the same powers and intensity as copper to the 'other end, the zinc immediately bethe magnetism of its south pole, if we test these gins to dissolve in the acid; and simultaneously by their action on a third body, such as a piece of with this solution of the metal, and the evolution non-magnetic iron. But if we try two bar-mag- of hydrogen from the water, electricity in its twonets against each other, we find that the south pole fold form is developed. At the middle point in of the one attracts the north, but repels the south the liquid between the two immersed plates we pole of the other, and vice versâ ; and if a north may suppose the electricity to come into existence, and south pole be placed together, instead of the -likening it as before to a double-headed arrow. magnetism being doubled in intensity, it is reduced Elongating themselves in directly opposite direc
tions through the liquid, the one arrow-head | ence bears testimony to the fact that we cannot speedily reaches the copper plate on the one side, alter the arrangement of the component parts of a and the other arrow-head the zinc on the other. mass, without inducing a corresponding change in The arrow at the copper is positive electricity. If the qualities of the mass those atoms build up. we speak of it as before, we shall say that a cur- Soot and wood-charcoal, coke and black lead, ove rent of positive electricity flows from the copper their different properties merely to a different aralong the telegraph wire to Edinburgh, and then rangement of identical particles of carbon ; and a returns to the zinc plate, where it may be regarded further modification of these invests them with as stopping :- :-at the same time that a current of the utterly diverse and characteristic attributes of negative electricity travels from the zinc plate along the diamond. But the electrical differences be the same telegraph wire, in an opposite direction tween two wires, one acting as an electrical conto that taken by the positive current, and may be ductor, and the other not, surely are not greater considered as ending at the copper plate.
than the optical differences between a lump of coke According to this view, the narrowest telegraph and a diamond crystal-or between carbonate of wire may be compared to a railway with two sets lime, uncrystallized in chalk, and crystallized in of rails, along which trains (of positive and nega- pellucid Iceland spar. We can set no limits, intive electricity) travel in opposite directions—in deed, to the extent to which modification of molecuobedience to a statute which requires that there lar arrangement will affect the properties of a mass. shall always be two opposite trains moving at the Nor is it any objection to such a view, that a same time along the rails. We must further metallic wire is a rigid solid, the component particles regard the wire, whilst conveying electricity, as of which are so locked together as not to admit of traversed, not by solitary engines or a few carriages, motion upon each other, or change of relative but by trains occupying the entire length of the position. The opinion once entertained, that only railway-fresh carriages constantly setting off at liquids and gases permit the mobility requisite for the one end, and being detached at the other. alteration in molecular arrangement, is now univer
The necessity, however, for the double wire, is sally abandoned. And, indeed, the expansion and best seen when we revert to the notion of electric contraction of a mass of metal under the influence ity travelling like a flying arrow. The route of of heat and cold is a sufficient refutation of it. the arrow is the wire, and the latter must be double, The Menai tubular iron bridge creeps, like a huge because the arrow itself is not an English cloth- snake, backward and forward several inches during yard shaft, which flies only in one direction ; but the twenty-four hours of a midsummer day. The such a two-forked thunder-bolt as the Greek sculp- massive glacier changes, from an aggregate of tors placed in the clenched hand of Jupiter Tonans, minute crystals of packed snow, into a mountain of which shoots east and west or north and south at clear ice. Every school-boy is familiar with the the same time, and the one bolt of which will not same phenomenon as developed during the formafly in one direction unless the other is equally free tion of a slide on a surface of snow. In copper to move in the opposite direction.
mines, an iron hammer, dropped into a pool satoWhat evidence, it may here be asked, is there rated with cupreous salts, is found, after the lapse to show that anything substantial moves along the of years, converted into a hammer of copper :telegraph-wires ? To this, as already implied, the whole of the iron has been extracted, and its there is but one answer. No actual proof can be place supplied, to the very centre, by coppergiven of the passage of anything material. The without the form or the bulk of the solid having flowing currents and the flying arrows are both altered during the process of transmutation. Durpurely imaginary—though the one is an hypothe- ing the production of steel from iron, in like mansis, and the other but an illustration. But there ner, the latter is embedded in charcoal powder, and is yet another mode of explaining the apparent the whole made red hot. The charcoal then penepassage of this invisible agent. It is, to be sure, trates into the solid iron, and impregnates its entire quite as hypothetical as the other two; but it is, mass. on the whole, more likely to be true; and it is These examples (and many more might be therefore now preferred by most men of science. added) apply to alterations in the structure of solid Our discussion would consequently be incomplete masses, much greater than we need assume to if we did not refer to it.
occur in an electrical conductor. So that we need According to this view, the metallic conductor, not hesitate to admit as possible, molecular changes such as the telegraph-wire which connects the ter- of a more simple character. The change that minal plates of the voltaic battery, is not a high- probably happens in the telegraph-wire is believed way along which electricity travels ; but the to resemble what we can pretty confidently affirm wire exhibits electrical phenomena throughout its to take place in magnetized iron, where the characentire length, only because its connection with the teristic phenomena are more readily observed, and zinc and copper wetted by the acid, produces, for are more familiar than in the case of electrical the time, a new arrangement of its own particles conductors. A bar-magnet, or compass-needle, or molecules, which invests the wire with new appears at first sight to possess magnetic powers properties—those, namely, which we call electri- only at each end, or pole. On closer examination, cal. Nor is there anything extreme or anomalous however, it is found to possess the opposite northin this assumption. The whole of physical sci- ern and southern magnetisms, in alternate succes
sion throughout its entire length. We may com- passed along the line. No man has stirred further pare it to one of the lines or stripes of a chess than to observe the flag shown him by his neighboard, or tesselated pavement, made up of alternate bor on the one side, and to show a corresponding colored pieces. The colors, however, must be flag to his neighbor on the other. The flag disonly two-for example, blue and yellow : the first played at Edinburgh was there from the first, square, or tessera, being of the one color, and the though unfurled, and remains there concealed, till last of the other. A piece of non-magnetic iron the next message is telegraphed from man to becomes temporarily magnetic if brought into the man. neighborhood of a permanent magnet, such as a * The arrangement described in the text, of alternate loadstone ; and while thus magnetic, the iron oppositely magnetic or oppositely electrical particles, is an exhibits the same alternation of oppositely mag- dle exliibits magnetic polarity; a voltaic battery or elec
example of what is called Polarization. A compass-neenetic particles which the compass-needle does. trical conductor, electric polarity. We have hitherto We may liken non-magnetic iron 10 an aggregate Block rather than a help, in the exposition of the physical
avoided the word, because it has proved a stumbling. of compound green particles. It becomes magnetic sciences, to those who do not make them a special study: in consequence of each of these separating into a A few words, however, in explanation of the “idea of blue and a yellow particle—which follow each polarity” inay he given here. The terms, " to polarize,"
polarization,” and “polarity," are taken from the comother alternately in rows. When the iron ceases pass-needle, the extremities of which pointing, the one to be magnetic, in consequence of the withdrawal in the north pole of the earth, the other to the south pole, of the loadstone, the result is as if the blue and needle, or magnet. The largest magnet, moreover, ap
have long been distinguished as the poles of the compassyellow particles united again, and the whole became pears to consist of a multitude of smaller magneis, uniformly green. In like manner the wire which arranged in rows end to end. The magnetic properties
of the hugest maguet are thus referred to its consisting connects the zinc and copper of a voltaic battery throughout its entire mass of particles, erch of wbich if is believed, in consequence of its junction with detached would exhibit a north and surih pole. If this these metals whilst they are affected by the acid, polar arrangement be destroyed, all magnetic phenomena
cease. Thus, if a loadstone he approached to a piece of to have induced upon it, throughout its entire soft iron it polarizes it, or induces in it mag.ietic polarlength, a succession of alternate electro-positive ity. In other words, the loadstone develops alternate
north and south poles in the iron, and this polarization of and electro-negative points, or particles possessed the particles of the metal continues as long as the loadof positive and negative electricity respectively. stone is in its neighborhood. The arrangement is of exactly the same kind as
The idea, suggested by magnetic phenomena, of alter
nale poles, is transferred to electricity as well as to other that of the magnetic bar-only it is an alterna- forces--with an important restriction, however, the overtion, not of the opposite magnetisms, but of the looking of which is the great cause of the unintelligibility
10 general readers of all references to polarity. opposite electricities. They remain separate so
In its extended sense, the term carries with it only the long as the constraining force of the battery is conception of an alternation of particles, or points, (centres exerted upon them ; but the instant the wire is dis- of force,) possessed of opposite powers-without including
the idea of those particles having a directive tendency in connected from it, the separate electricities unite, space, so thar they take up positions in relation to the poles and all electrical phenomena cease.
of the earth. Thus the polarity of light is evidenced in liken the telegraphi-wire, when disconnected from that of electricity in a third, that of chemical_offinity
one class of phenoinena, ihe polarity of heat in another, the battery, to a thread on which purple beads are (which, however, is perhaps identical with electrical strung together, as on a necklace. When the polarity) in a fourth, that of crystalline affinity in a fifth. wire is connected with the battery, each purple ical affinity, and crystalline affinity, all agree with mag.
But light, (polarized) heat, (polarized) electricity, chembead separates into a red (positively electric) and netism, in manifesting their powers, not as single, but as blue (negatively electric) one. The red and blue 1w0-fold forces ; and are all characterized by the exhibi.
tion, side by side, of two agencies, the same in nature, beads now succeed each other alternately along the vet opposite in the mode of their manifestation. Thus line; and remain separate, whilst, in the language positive and negative eleciricity have each a power of alof another theory, electricity is passing ; but they the same intensity, and regulated by the same laws--ex:
iraction and a power of repulsion, of the same kind, of coalesce again into the compound purple spheres, cept that in the circumstances where the one electricity so soon as the connection with the battery is inter- exhibits attraction, the other exhibits repulsion, and vice
versâ. And, in like manner, a ray of polarized lighi, or rupted.
heat, a row of magnetized or electritied molecules, or a row According to this view, there is no travelling of of atoms under the influence of chemical affinity or crys: electricity charged with messages from one station talline agency, agree in the manifestation of a twofold
force, exhibiting itself in the alternation of oppositely to another. The message telegraphed from Lon- endowed points or particles. don to Edinburgh is not wafted by electricity
This common character is now denoted by saying that which speeds from the former, inscribes its hiero- they all exhibit polarity ; nor have we any other term in
our language possessing the same signification. It is glyphics at the latter as it rushes past, and feets much to be regretted, therefore, that its value has been back to London ; but the telegraph-wire, with in- lessened by its vague employment. By many it is used to
denote the mere antagonism of two forces. Man, for exconceivable rapidity, merely arranges its own con- ample, is said to exhibit polarity, because he is possessed stituent particles, from end to end, in alternate of soul and body! And though such language might be conelectro-positive and electro-negative molecules ; it is not competent to one who regards mind and matter as
sistent in the mouth of a pire idealist, or a pure materialist, and the index on the Edinburgh dial plate is essentially distinct. Polarity is not merely ihe antagonism affected only by the small portion of the wire or dualistic development of two unlike forces.
keep a mass of iron suspended either by a loadstone or by which surrounds the gnomon. It is as if a row a spring, or by the inuscular exertion of an animal
. And of men were placed side by side from Edinburgh here we have ihree examples of the antagonistie manifesto London, with signal-flags in their hands. The tation of two forces -- gravity and magnetism, gravity and
elasticity, gravity and vital force. But none of those are flag shown as a signal at Edinburgh has not been exhibitions of polarity. It is the antagonistic or dualistic