His work was mainly concerned with electricity and magnetism, though he also made some contributions to optics and physiology.
It was suggested again and again as each new discovery in electricity and magnetism seemed to render it more feasible.
Some of the principal phenomena of magnetism may be demonstrated with very little apparatus; much may be done with a small bar-magnet, a pocket compass and a few ounces of iron filings.
This retardation was still more pronounced in the case of tungsten-steel, which lost its magnetism at 910° and remained nonmagnetic till it was cooled to 570°, a difference of 240°.
It is on the service that he rendered to science in establishing the relations between electricity and magnetism, and in developing the science of electromagnetism, or, as he called it, electrodynamics, that Ampere's fame mainly rests.
He invented magnets that could withstand the effects of percussion and ordinary temperature variations.
The distribution of magnetism and the position of the poles in magnets of other shapes, such as cylindrical or rectangular bars, cannot be specified by any general statement, though approximate determinations may be obtained experimentally in individual cases.'
A bar of soft iron introduced into the coil is at once magnetized, the magnetism, however, disappearing almost completely as soon as the current ceases to flow.
Within a limited space, such as that contained in a room, the field due to the earth's magnetism is sensibly uniform, the lines of force being parallel straight lines inclined to the horizon at the angle of dip, which at Greenwich in 1910 was about 67°.
An explanation of the twist has been given by Maxwell (Electricity and Magnetism, § 448).
Electrostatics and Magnetism, p. 236.
He also engaged in work on magnetism, the polarization of light, phosphorescence and the absorption of light in crystals.
In Englishspeaking countries the ore is commonly known as magnetite, and pieces which exhibit attraction as magnets; the cause to which the attractive property is attributed is called magnetism, a name also applied to the important branch of science which has been evolved from the study of phenomena associated with the magnet.
If the bar inserted into the coil is of hardened steel instead of iron, the magnetism will be less intense, but a larger proportion of it will be retained after the current has been cut off.
If the iron is soft and fairly pure, it loses its attractive property when removed from the neighbourhood of the magnet; if it is hard, some of the induced magnetism is permanently retained, and the piece becomes an artificial magnet.
The equation F = B 2 /87r is often said to express " Maxwell's law of magnetic traction " (Maxwell, Electricity and Magnetism,, §§ 642-646).
A more precise definition is the following: When the magnet is placed in a uniform field, the parallel forces acting on the positive poles of the constituent filaments, whether the filaments ' For the relations between magnetism and light see Magnetooptics.
Effects Of Mechanical Stress Upon Magnetization The effects of traction, compression and torsion in relation to magnetism have formed the subject of much patient investigation, especially at the hands of J.
When the oscillations pass through the coil they annul the hysteresis and cause a change of magnetism within the coil connected to the telephone.
Magnetism may be imparted to a bar of hardened steel by stroking it several times from end to end, always in the same direction, with one of the poles of a magnet.
Steel articles, such as knitting or sewing needles and pieces of flat spring, may be readily magnetized by stroking them with the bar-magnet; after having produced magnetism in any number of other bodies, the magnet will have lost nothing of its own virtue.
Maxwell, Electricity and Magnetism, § 7 H.
At a later period he was one of the leading contributors to the Encyclopaedia Britannica (seventh and eighth editions), the articles on Electricity, Hydrodynamics, Magnetism, Microscope, Optics, Stereoscope, Voltaic Electricity, &c., being from his pen.
Inside a magnetized body, B is the force that would be exerted on a unit pole if placed in a narrow crevasse cut in the body, the walls of the crevasse being perpendicular to the direction of the magnetization (Maxwell, § § 399, 604); and its numerical value, being partly due to the free magnetism on the walls, is generally very different from that of H.
Denoting the distance AM by d 1, BM by d2, and AB by 1, we have for the force at M due to the magnetism of the rod H P =d 12 - horizontal component (dla - d 2 3).
Upon the magnetism of iron, while the presence of only 2.25% was comparatively unimportant.
(Maxwell, Electricity and Magnetism, II., § 437).
Joubert, Electricity and Magnetism, §§ 3 8 4, 39 6, 1226; A.
The fact being established that magnetism is essentially a molecular phenomenon, the next step is to inquire what is the constitution of a magnetic molecule, and why it is that some molecules are ferromagnetic, others paramagnetic, and others again diamagnetic. The best known of the explanations that have been proposed depend upon the magnetic action of an electric current.
It was occasioned by the discharge of the Macedonian veterans, and only the personal magnetism of Alexander and his threat to entrust himself altogether to the Orientals availed to quell it.
Steel is much more retentive of magnetism than any ordinary iron, and some form of steel is now always used for making artificial magnets.
This experiment proves that the condition of magnetization is not confined to those parts where polar phenomena are exhibited, but exists throughout the whole body of the magnet; it also suggests the idea of molecular magnetism, upon which the accepted theory of magnetization is based.
Among other researches relating to atomic and molecular magnetism are those of 0.
Hartog has endeavoured to show that it can only he formed by a dual force, analagous to that of magnetism, the spindle-fibi es being comparable to the lines of force in a magnetic field and possibly due to electrical differences in the cell.
Until 1820 all the artificial magnets in practical use derived their virtue, directly or indirectly, from the natural magnets found in the earth: it is now recognized that the source of all magnetism, not excepting that of the magnetic ore itself, is electricity, and it is usual to have direct recourse to electricity for producing magnetization, without the intermediary of the magnetic ore.
At shorter distances the magnetism induced in the weaker magnet will be stronger than its permanent magnetism, and there will be attraction; two magnets with their like poles in actual contact will always cling together unless the like poles are of exactly equal strength.
An actual magnet may generally be regarded as a bundle of magnetic filaments, and those portions of the surface of the magnet where the filaments terminate, and socalled " free magnetism " appears, may be conveniently called poles or polar regions.
A magnet which consists entirely of such solenoids, having their ends either upon the surface or closed upon themselves, is called a solenoidal magnet, and the magnetism is said to be distributed solenoidally; there is no free magnetism in its interior.
A magnet which can be divided into simple magnetic shells, either closed or having their edges on the surface of the magnet, is called a lamellar magnet, and the magnetism is said to be distributed lamellarly.
The force acting on the magnetism of one of the faces, and urging this face towards the other, will be less than B by 27r1, the part of the total force due to the first face itself; hence the force per unit of area with which the faces would press against each other if in contact is P = (B-27rI)I =27rT 2 +HI = (B 2 -H 2) =/81r.
The width of the gap may be diminished until it is no greater than the distance between two neighbouring molecules, when it will cease to be distinguishable, but, assuming the molecular theory of magnetism to be true, the above statement will still hold good for the intermolecular gap. The same pressure P will be exerted across any imaginary section of a magnetized rod, the stress being sustained by the intermolecular springs, whatever their physical nature may be, to which the elasticity of the metal is due.
Maxwell (Electricity and Magnetism, § 444), recognizing that the theory in this form gave no account of residual magnetization, made the further assumption that if the deflection of the axis of the molecule exceeded a certain angle, the axis would not return to its original position when the deflecting force was removed, but would retain a permanent set.
Thomson, Electricity and Magnetism, § 205.
These observations have an important bearing upon the molecular theory of magnetism, which will be referred to later.
If a transverse cut is made through a bar whose magnetization is I and the two ends are placed in contact, it can be shown that this force is 27r I 2 dynes per unit of area (Mascart and Joubert, Electricity and Magnetism, § 322; and if the magnetization of the bar is due to an external field H produced by a magnetizing coil or otherwise, there is an additional force equal to HI.
An angle e with the normal, the normal component of the magnetization, I cos e, is called the surface density of the magnetism, and is generally denoted by a.
The factor of proportionality will be I-41r, so that ' The principal theoretical investigations are summarized in Mascart and Joubert's Electricity and Magnetism, i.
69-94; Mascart and Joubert, Electricity and Magnetism, ii.
Effects Of Temperature Upon Magnetism High Temperature.
In 1868 he obtained the same professorship at Edinburgh University, and in 1873 he published a textbook of Magnetism and Electricity, full of original work.
The opposite and parallel forces acting on the poles are always equal, a fact which is sometimes expressed by the statement that the total magnetism of a magnet is zero.
For many experiments the field due to the earth's magnetism is sufficient; this is practically quite uniform throughout considerable spaces, but its total intensity is less than half a unit.
Molecular Theory Of Magnetism According to W.
"The earth," he adds elsewhere, "especially if fresh, has a certain magnetism in it, by which it attracts the salt, power, or virtue (call it either) which gives it life, and is the logic of all the labor and stir we keep about it, to sustain us; all dungings and other sordid temperings being but the vicars succedaneous to this improvement."