Lectures on popular and scientific subjects

by 14th earl of James Sinclair Caithness

Magnetism.—Unlike electricity, which acts with a shock and then expires, magnetism is a constant quantity, and constant in its action; and it has this singular property, that it can impart itself as a permanent force to bodies previously without it. Thus, there being natural magnets and artificial, we can, by passing a piece of steel over a magnet, turn it into a strong magnet itself; although we can also, when it is in the form of a horse-shoe, by a half turn round and then rubbing it on the magnet, take away what it has acquired, and bring it back to its original state. The magnetic property is very readily imparted (by induction, as it is called) to soft iron, but when the iron is removed from the magnetising body, it parts with the virtue as fast as it acquired it. To obtain a substance that will retain the power induced, we must make some other election; and hard steel is most serviceable for conversion into a permanent magnet.

The properties of the magnet are best observed in magnetised steel; and when we proceed to test its magnetic power, it will be found that it is most active at the extremities of the bar, which are hence called its poles, and hardly, if at all, at the centre; that while both poles attract certain substances and repel others, the one always points nearly north and the other nearly south when the bar is horizontally suspended; and that, when we break the bar into two or any number of pieces, however small, each part forms into a complete magnet with its virtue active at the poles, which, when suspended, preserves its original direction; so that of two particles one is, in that case, always north of the other; nay, it is probable that each of these has its north pole and its south, as constant as those of the earth itself, which, too, is a large magnet.

The magnet acts through media and at a distance, as well as in contact; and it has an especial attraction for iron, the more so when the conducting medium is solid, such as a table; and so when the magnet is horizontally suspended, or poised, in the vicinity of iron, its tendency to point north and south is seriously disturbed. The disturbance of the bar, or needle, in such a case, is called its deflection; and it is corrected by so placing a piece of soft iron or another magnet in its neighbourhood as to neutralise the effect, and leave said bar, or needle, free to obey the magnetism of the earth. The needle, it is to be remarked, does not point due north and south, neither, when poised freely on its centre, does it lie perfectly horizontal; in our latitude it points at present 20° west of north, which is called its declination, and its north pole slopes downwards at an angle of 68°, which is called its dip.

By holding a rod of iron, or a poker, for a length of time parallel to the direction of the needle, so as to have the same declination and the same dip, it will gradually assume and display magnetic virtue, and this will ere long become fixed and powerful under a succession of vibratory shocks. There is a beautiful experiment in which a needle, when magnetised, can be made to float on water, when it adjusts itself to the magnetic meridian, and will incline north and south the same as the needle of the compass.

The Chemical Action of Electricity and Magnetism.—These agents possess powers which develop wonderfully in connection with chemical combination. Thus, if we suspend a piece of iron in a vessel which contains oxygen gas, and apply to the metal an electric current, it will immediately begin to unite rapidly, and form an oxide with oxygen, emitting, during the process, intense heat and a bright flame. Zinc, too, when similarly acted on, will ignite in the common atmosphere and burn away, though with less intensity, till it also is, under the electric force, reduced to an oxide. It is presumed that many other chemical combinations take place because of the simultaneous joint development of electric agencies, as in copper, water, and aquafortis, nitrate of copper, &c. So also it happens that, when a plate of iron is for some time immersed in a copper solution, it comes out at length covered over with a coating of copper. And it is because there is electricity at work that a silver basin will be coated with copper when we pour into it a copper solution, and at the same time place in it a rod of zinc, so that it rests on the side and bottom, though no coating will form at all when there is no rod present to excite the electric current. The same phenomena will appear if we deposit a silver coin in the solution in question: the coin will come out unaffected, unless we excite affinity by means of a rod of iron. It is under the action of an electric current that one metal is coated with another. The metal, copper say, is steeped in a solution of the coating substance, and connected by means of wires with a galvanic battery, under the action of which the metal in solution unites with the surface of the plate immersed in it. Heat also is developed under magnetic influence, and that often of great intensity. Thus, if we connect the poles of a voltaic battery by means of a platinum wire, heat will develop to such a degree that the platinum will almost instantaneously become red hot and emit a bright light, and that along a wire of some considerable length. A similar effect is noticeable when we substitute other metals, such as silver or iron, for platinum. And the electric light, which flashes out rays of sunlike brilliance, is the result of placing a piece of compact charcoal between the separated but confronting poles of a powerful galvanic battery, light, developing more at the one pole and heat more at the other of the incandescent substance.

Kindred, though much milder, results will show themselves under simpler, though similar, contrivances. A flounder will jump and jerk about uneasily if we lay it upon a piece of tinfoil and place over it a thin plate of zinc, and then connect the two with a bent metal rod; which will happen to an eel also, if we expose it to a gentle current from a battery.

By means of electric or magnetic action we can separate bodies chemically combined, as well as unite them into chemical compounds; as will appear if we place a piece of blotting paper upon tinfoil, and this upon wool; if we then spread above these two pieces of test-paper, litmus and turmeric, the one the test of acids, and the other of alkalis, and saturate both with Glauber salt (which is by itself neither an acid nor an alkali, but a combination of the two), and, finally, connect each by means of a piece of zinc with the poles of a battery, the test-papers will immediately change colour, as they do the one in the presence of an acid simply, and the other of an alkali simply, but never in a compound where these are neutralised; thus proving that the compound has in this case been decomposed, and its elements disintegrated one from another.

A very powerful magnet can be produced by coiling a wire round a bar of soft iron, and attaching its extremities to the poles of a galvanic battery, when it will be found that its strength will be proportioned to the strength of the current and the turns of the coil. This is especially the case when the bar is bent into the form of a horse-shoe, and the wires are insulated and coiled round its limbs. The force communicated to a magnet of this kind, which is often immense, is the product of the chemical action which goes on in the battery, and, in a certain sense, the measure of it. How great that is we may judge when we consider that, evanescent as it is in itself, it has imparted a virtue which is both powerful and constant, and ever at our service.

Summary.—Thus, then, on a review of the whole, we find all things are endowed with attractive power, and that there is no particle which is not directly or indirectly related, in manifold ways, to the other particles of the universe. There is, first, the universal attraction of gravitation, under which every particle is, by a fixed law, drawn to every other within the sphere of existence. There is, secondly, the attraction of cohesion or aggregation, which acts at short distances, and unites the otherwise loose atoms of bodies into coherent masses. There is, thirdly, the power by which elements of different kinds combine into compounds with new and useful qualities, known by the name of chemical affinity. And, lastly, related to the action of affinity, aiding in it and resulting from it, there are those strange negative and positive, attractive and repellant polar forces which appear in the phenomena of electricity and magnetism, agencies of such potency and universal avail in modern civilisation.

On the permanency of such forces and their mutual play the universe rests, and its wonderful history. With the collapse of any of them it would cease to have any more a footing in space, and all its elements would rush into instant confusion. What a Hand, therefore, that must be which holds them up, and what a Wisdom which guides their movements! Verily, He that sends them forth and bids them work His will is greater than any one—greater than all of them together. How insignificant, then, should we seem before Him who rules them on the wide scale by commanding them, while we can only rule them on the small by obeying them! And yet how benignant must we regard Him to be who both wields them Himself for our benefit and subjects them to our intelligence and control!