On examining other bodies, it was found that every known sub stance when brought under the influence of a powerful electromagnetic force, assumed either an axial or an equatorial position with respect to the poles. Faraday was led to regard all substances in nature as magnetic : those bodies which took up an axial position, or were attracted by the poles, he termed paramagnetic, while those bodies which were repelled, and consequently took up an equatorial position, he termed die-magnetic. A piece of hmmatitic iron ore which is not acted on by an ordinary magnet will point axially when suspended between the poles of an electromagnet; and a sheet of writing-paper rolled up into a short cylinder will also point axially in consequence of the minute portion of iron or of cobalt which it contains. The salts of the magnetic metals, when the latter form the base, were also found to he magnetic, such for example as crystals of proto-sulphate of iron, and solutions of such salts in water contained in a thin glass tube (the glass not being magnetic) assumed an axial position. Solutions of sulphate of nickel and sulphate of cobalt behaved iu a similar manner and the salts of chromium and manganese were also found to be mag netic, whence it was inferred that the metals themselves are so. A stick of phosphorus assumes the equatorial position, as do also bismuth and antimony ; and organic substances, such as slices of wood, apple, potato, flesh, &c. These are are diamagnetic, but not strongly so. Sulphur and india-rubber are decidedly repelled. Among liquids, alcohol and ether are diamagnetic, and water still more so. Even the different gases and vapours were found to be acted on by the magnet, and among other modes of showing the action, soap-bubbles were blown with each gas in succession upon the cud of a capillary tube, and being suspended near the pole of the magnet the circuit was com pleted, when the bubble was attracted or repelled according as the gas was magnetic or diamagnetic. Oxygen was found to be powerfully magnetic : all other gases were found to be diamagnetic, with the ex ception perhaps of nitrous oxide. Elevation of temperature was found to increase the diamagnetic condition, a stream of hot oxygen being diamagnetic in an atmosphere of cold oxygen. Faraday has suggested that this diminution of oxygen in magnetic intensity, as the tempera ture rises, may account in some way for the diurnal variations of the needle. A diminished pressure was found to lower the diamagnetic force; the magnetic power of oxygen being diminished by a diminu tion of density. Nitrogen, which is a diamagnetic, does not seem to undergo any change in its magnetic relations, by variations in density and temperature. In experiments of this nature the gases were enclosed in thin glass tubes in connection with a delicate torsion balance. The flame of burning bodies, as of a taper for example, when
plated between the poles of the magnet is repelled towards either side, and even divides into two streams which pass off horizontally, one on either side, in the equatorial direction.
It is Important to observe, that the nature of the medium in which a trubetanee is pieced, has an influence on the magnetic condition of nutter ; thus a rod of glass suspended horizontally in water, which is du-magnetic, will point axially, but if the same rod be suspended iu a solution of sulphate of in-n, which I. magnetic, it will point 'qua terially. So also, a tube filled with a solution of sulphate of iron, will appear to be magnetic if placed In pure water, but if placed in it stronger solution of rulplutte of iron, it. will be diaeinagnetic. The same body may also be maga-tie or die-magnetic, acconling as it forme the bare or electreepositive constituent of a compound, or the acid or electronegative conetituent. Iron for example, in the crystals of green vitriol acts as a base, and makes the crystals magnetic, but in the yellow prusedate of potash, where the iron is not a base but an electro negatirteconatituent, the cr.) totals are diamagnetic; so also bichromate of putaah is dlemagnatio, the chromium acting the part of an acid, while sulphate of chromium is magnetic, for here chromium acts as a base. Tyndall and Knoblauch (' Phil. Mag.' 1850), have shown that the arrangement of the component particles of a body will determine whether it be magnetic or diaenagnetio. For example, carbonate of iron is magnetic; if reduced to fine powder and formed into a cylinder by means of gum-water, it will point axially, but if oompressed into a plate, this plate will set with its faces parallel to the equatorial direction. In fact, the parte brought nearest together by compresaion, were those which exhibited the diamagnetic, or the magnetic action most strongly. In this way the phenomena, dis covered by Plucker, were accounted for that in doubly refracting crystals the optic axis assumes a definite direction under the influence of the electromagnet; for it is along this axis that the greatest condensation of the particles has probably taken place. There are many other re markable circumstances connected with diamagnetism, for which we must refer to Faraday's original memoirs, which have been published in a collected form, and also to Tyndall's papers, especially those in tho ' Philosophical Transactions' for 1855, in which it is shown among other results, that the dia-magnetic repulsion, as measured by the torsion balance, is as the square of the intensity of the current.