Magnetism
3 of the 7 encyclopedias on this shelf carry an entry for Magnetism. Both are reproduced below, so you can see where they agree and where they differ.
American Watchmaker and Jeweler (1892)
The agent or force in nature which gives rise to the phenomena of attraction, polarity, etc., exhibited by the loadstone, magnet, etc. A watch will become magnetized by too close proximity to a powerful magnetic field, such as is developed in a dynamo electro machine, for producing electric light, or by coming in contact with an ordinary magnet, as well as other sources of magnetic or electro-magnetic influences, and by these means all its steel parts become permanent magnets. Each piece of steel has then assumed definite polarity, so that if it is balanced on a point like a compass, it will, like the latter, indicate the direction of the earth's magnetic poles. The influence of these separate magnets, one on the other, and the influence of the earth's magnetism on the different parts, become very potent disturbers of time, keeping. Hairsprings, balances, and other small steel parts often become magnetized through being handled with magnetized tweezers or being placed near or in contact with other steel tools that have been magnetized. Mr. B. Frese exemplifies the influence of the separate magnets produced in a watch by its parts becoming magnetized as follows: if we take two compasses and place them side by side, so that the two bearing points of the needles will form a right angle to their direction, neither of them will show any variation from their natural position or the position they are compelled to take by the influence of the earth's magnetism; but by moving one a little to the North or South of this position, we notice a deflection in both, which is caused by the poles of unequal names having been brought near to each other. Besides this main disturbing influence upon accurate time keeping, we must also consider the disturbance caused by direct attraction, which takes place by two magnetized parts when their equal, as well as their unequal, polarities come close together, but when two extremities of equal polarity come close together or in contact, the stronger magnetized piece will cause the weaker to assume its own polarity, so that when the South polarity of a strongly magnetized piece is brought in contact with the South polarity of a weaker, the South of the latter will be changed to North, and the North to South when the two North polarities have been in contact. The largest steel parts in a watch are the mainspring and the case springs, and these are, therefore, the most potent to cause a disturbance in a steel or compensation balance, aside from the earth's magnetism; the balance being the medium by which nearly all the disturbance is caused, as during its vibrations it makes different positions to the polarities of the other steel parts, as well as the earth's polarities, which is the greatest disturber, aside from the mainspring, the polarities of which change in relation to the balance as the watch runs down. The force one magnetized piece exerts on the other multiplies with decreased distance. The fork, pallets and 'scape wheel are too small in bulk to cause much disturbance, either by direct attraction or directive force, unless they are charged to saturation, which very seldom occurs. If a magnetized balance is placed on a poising tool, with the staff in North and South direction, it will appear out of poise, caused by the earth's magnetism, and will maintain its North polarity uppermost. If it is placed in an East direction, it will no longer allow the North polarity to remain uppermost, but will cause the same to move toward the North and indicate the magnetic dip, the amount of which varies in the different latitudes of the globe. If we place the balance in a horizontal position, its north and South polarities will coincide with those of a compass, showing that if the balance were the only part magnetized in a watch, that magnetism caused more complicated variations than a balance out of poise to the same extent. That trying to poise a magnetized balance would be useless, is self-evident, for the reason that in a horizontal and North and South position, no equilibrum can be obtained. The influence of magnetized parts that do change position in a watch, is a constant one, as long as the size of vibration is maintained, and is, therefore, not the cause of serious disturbance. The substituting of new case springs will, therefore, be of little or no benefit. To detect magnetism, place a pocket compass upon a show case, and place the watch to be operated upon on the table and close to the compass, and to the East and West of it. Before starting the test, stop the watch, and keep it from running by inserting a wedge made from a thin slip of paper beneath the balance. Turn the compass box around until the needle points to zero, before approaching the watch to it. Having placed the watch to the East or West of the compass, proceed to turn the movement, presenting first one figure of the dial and then another to the compass, and at the same time noting the deflection of the compass needle. Note whether the deflection is towards the East or West, i.e., whether it repels or attracts the needle. If the movement is not magnetized, the compass needle will remain stationary. If it is magnetized, the needle will be deflected, and by noting the spot, you can very readily detect the magnetized part. Magnetism may be removed from small steel parts by placing them in the lathe and revolving them rapidly, and at the same time approaching them with a horseshoe magnet, and then gradually withdrawing the magnet. It is not good policy, however, to place any magnetized piece in your lathe, as you are liable to magnetize chucks, and they will cause you no end of trouble in the future. Demagnetizers are now to be purchased so cheaply that it will scarcely pay you to experiment with home made substitutes. See Demagnetizer.
Collier's New Encyclopedia (1921)
the science which treats of the phenomena exhibited by magnets-phenomena due to one of those forces w which, like , like electricity and heat, are known only by their effects. The phenomena of magnetism were first observed in the loadstone or magnet (so named from Magnesia in Asia Minor). The loadstone is a kind of iron ore (magnetic iron ore), and is found in many parts of the world, especially in the Scandinavian peninsula, and in Siberia. It has the power of attracting small pieces of iron and steel, and when suspended in such a way as to be able to move freely, always points to what are called the magnetic poles of the earth, that is nearly N. and S. A piece of loadstone forms a natural magnet, and has the further remarkable power of giving all its own properties to hard iron or steel when these bodies are rubbed by it. A bar or mass of iron or steel to which the peculiar properties of a natural magnet have been imparted by friction from other magnets or by electric induction is called an artificial magnet. When freely suspended, all magnets, natural and artificial, rest with their lengths in a N. and S. direction, and this property is utilized in the well-known compass. They attract iron and other magnetic substances with a force increasing from the middle of the magnet to its extremities, which are called its poles. The magnetism at the two poles is different, that pole which points to the N. is distinguished as the north or north-seeking or austral pole, or by the sign plus (+); that which points to the S. as the south or south-seeking or boreal pole, or by the sign minus (-). The poles of the same denomination repel each other, while those of different names have mutual attraction, thus resembling the two electricities, positive and negative. The intensity of this attraction and repulsion varies inversely as the square of the distance, a law which also governs electrified bodies. Magnetism pervades the earth as electricity does the atmosphere. It assumes a totally different form in different substances; the metals iron, nickel, and cobalt being strongly attracted by the magnet; others such as bismuth, copper, silver, gold, etc., being as strongly repelled (see DIAMAGNETIC). The space in the neighborhood of a magnet is called the magnetic field; a piece of soft iron brought into this space becomes magnetic, although it loses its magnetism as rapidly on removal from the field. (See INDUCTION.) Steel has great coercive force, in virtue of which it requires time for magnetization, and retains its magnetism on removal from the field. Hard steel may be made magnetic by rubbing it several times in the same direction with a powerful magnet, and hence it is easy to multiply magnets. The most powerful permanent magnets are produced by rubbing bars of steel on electromagnets (see ELECTRO-MAGNETISM), or by moving them backward along the axis of a coil of wire in which an electric current is passing. A bar is magnetized to saturation when its magnetism is as great as it can retain without future sensible loss. Terrestrial magnetism, which pervades the whole earth, is extremely complicated. It becomes manifest by its influence on the magnetic needle, varying with the time and place over the earth. One pole of the needle points toward the N., the other toward the S. There are, however, only two lines on the surface of the earth on which it points directly N. and S., and where the magnetic and geographical meridians appear to coincide. Elsewhere the needle deviates more or less from the true N. This is termed the declination of the needle, and varies from place to place, and in the course of time at the same place (see ISODYNAMIC). When a needle is balanced on a horizontal axis, so that it can turn in a vertical plane, the extremity attracted by the nearer magnetic pole of the earth points more or less downward (see DIPPING NEEDLE). The angle thus made is called the dip or inclination, and the lines marking equal inclinations on a map are called isoclinal lines. They intersect the isogonal lines, and the dip increases toward the perpendicular as the magnetic poles are neared. These magnetic poles do not coincide with the geographical poles, the N. being 70° 5' N., and 96° 43′ W. The S. is probably at 73½° S. and 14/½° E. There are two foci of maximum force in the Northern Hemisphere and two in the Southern. In the Northern Hemisphere the stronger focus is assumed to be in 52° N. and 90° W., and the weaker in 70° N. and 115° E. In the Southern Hemisphere the stronger focus is assumed to be in 65° S. and 140° E., and the weaker probably in 50° S. and 130° W.
Aiton's Encyclopedia (1910)
a force possessed by certain iron ores called lodestone. The lodestone was well known to the ancients. When a lodestone is brought in contact with a mixture of the fine particles of various materials, it will select and attract particles of iron and steel very noticeably. Nickel, cobalt, and a few others are attracted slightly. Bits of lead, copper, and wood are not attracted. If a bar of steel be brought into contact with the lodestone, especially if it be stroked from end to end, it acquires the properties of the lodestone itself, and will in turn attract particles of iron and steel. Such a bar is called a magnet. If placed on a piece of cork floating in water, or if suspended on a pivot so that it may revolve readily, it assumes a north and south direction, a property of which advantage is taken in the construction of the mariner's compass . The end of the magnet that turns north is called the north or positive pole; the opposite end is called the south or negative pole. The earth, itself, is a huge magnet. Its magnetic poles are in the Arctic and Antarctic zones, but do not coincide with the north and south geographical poles . The lodestone is thought to have become magnetized by the earth. We observe that masses of iron which remain stationary for any length of time become magnetic. For this reason, tools lying idle in a workshop become magnetized. A steel rod held in a position parallel to the dipping needle becomes magnetized. When a magnet is heated to redness, it loses permanently its magnetism. Red hot iron is not attracted by a magnet. Large electric magnets are used for unloading cars of scrap iron. The pieces of old iron cling to a large magnet like iron filings to the toy magnet. One magnet of this sort is used to load and unload steel rails, two tons at a time, and to lift steel ingots out of a ship. A magnet of this sort, suspended from a derrick, is capable of handling kegs of nails, seven at a load. See Compass ; Electro-Magnet