« PreviousContinue »
On the Fundamental State of the Magnetic Phenomena of the
Electrical Connecting Wire, or on the Transverse Electrical Charge. By M. Prechtel, Director of the Polytechnic Institution in Vienna. (Communicated by the Author.)
Magnetism produced by electricity is of the same nature as common magnetism; the apparently anomalous phenomena of electric magnetism may, therefore, be recognized in the pheno mena of the magnetism elicited by the earth's action, or by common magnetism; and these phenomena ought to include the explanation of the phenomena of electro-magnetism. Setting out from this principle, I have made experimental researches on transverse magnetization, the fundamental phenomena of which were previously unknown. I believe that these phenomena give a satisfactory explanation of the physical state of the electromagnetic connecting wire, and of electro-magnetic facts in general. I have discovered the following facts, which I have detailed in several memoirs, inserted in the first, fourth, and sixth numbers of M. Gilbert's Annales de Physique for the year 1821. These facts I shall now detail in succession.
1. When a straight iron wire has one of its ends presented to the magnetic pole, it is well known to be magnetized, or its two ends form magnetic poles of a certain degree of intensity. All circumstances being equal, this polarisation is more intense in a perfectly straight wire than in one which has angles and inequalities.
2. When an iron wire, which has its ends united accurately by welding, is magnetized in a mode presently to be described
New Series, vol. IV.
an endless magnet is formed, which possesses separate poles throughout its circumference, or heteronomous poles alternately succeeding each other. For these experiments the softest iron wire should be employed.
3. When the most perfect circular form is given to an endless wire, and it is suspended vertically, it will be found when examined by means of a very small magnet,* that the lower part has acquired a north pole, and the upper a south pole. By applying the pole of a magnet for some time to any part of this circular wire, it will be found that this ring is so magnetized, that its periphery presents two heteronomous poles diametrically opposite, as may be seen by Pl. XIII. fig. 1. i i are points of indifference. It sometimes happens that the heteronomous poles are placed from 90° to 90°, as in fig. 2; then the points of indifference are ii ii.
4. When an endless wire is bent in a quadrangular form, as in fig. 3, and it is magnetized by applying the heteronomous poles of a magnet to the angles a and b; then the four angles are magnetized in such manner that the heteronomous poles succeed each other alternately, as is shown by fig. 3. If the magnet is sufficiently strong, and the iron wire very soft and even, then this magnetic arrangement will take place by the application of a single magnetic pole to one angle, for example, to the angle b.
5. When an endless wire is bent in the form of an octagon, and we proceed as before, i.e. by applying the heteronomous poles of a magnet to the two angles a, b, fig. 4; the magnetic poles assume a similar arrangement, i. e. the heteronomous poles placed at the angles succeed each other alternately, or each north pole is followed by a south pole, or vice versa. This will take place in every polygon. If these magnetic arrangements be represented as in the figure, by arranging magnetic needles, one half of these needles will be directed to the right, and the other half to the left. These facts prove that magnetic polarity has a tendency to establish itself in a right line; and it is seen that in the endless polygonal magnet a simple magnetic impulse, upon a single point of its periphery, produces a quantity of heteronomous poles, which succeed each other alternately upon this periphery.
6. This arrangement of the needles indicates the elementary action of each side of the polygon; this side representing a linear magnet. Nevertheless this elementary action can be observed only when the sides of the polygon possess sensible length, so that a very small magnetic needle can follow the elementary or separate action of the side, or of this linear magnet. Let us suppose that these linear magnets, forming the sides of the polygon, are extremely small (1), which will happen when the diameter of the polygon is extremely small, or the number of its
• I find that small magnetic needles from half to one-eighth of an inch long, are extremely delicate in cases of small quantities of magnetism, even when the heterono mous poles are very near each other,
sides is very great, or which comes to the same, that the polygon of a given diameter becomes a circle; or (2) that the length of the magnetic needle employed to examine the polarity of the endless magnet is very great compared with the length of a side of tlie polygon; then this elementary action of each side of the polygon cannot be observed ; but the combined action of all the polarizations distributed on all the sides above the diameter parallel to the needle, will take place upon the magnet. By this combined action, the needle shows an apparent arrangement of the polarizations in the endless magnet. This happens, precisely in the same manner, in arranging a series of magnets in the manner represented by fig. 7. These magnets are disposed one after the other in such manner, that the heteronomous poles touch and follow each other alternately in the length a b. In examining the magnetic arrangement ab, by means of a very small magnetic needle, it will be observed that the elementary actions are represented in the figure by small needles. But in employing a magnetic needle which equals or exceeds the length of the line ab; this needle attracted by the combined action of all the polarities, and determined by the quality of the two extreme poles of this magnetic arrangement, will assume a constant direction. This arrangement indicated by the needle m n is only apparent, and we should deceive ourselves if we were to conclude from its position, that the arrangement a b is a common magnet, presenting its poles at the two extremities, and the point of indifference in the middle. Let us suppose that the line a b is extremely short, it will then be impossible to examine the partial actions, and we must be content with observing the total or apparent action.
7. It is nevertheless easy to observe what happens in a polygonal endless magnet with respect to the arrangement of the needle around its periphery, if the length of the sides of the polygon are very small when compared with the length of the examining needle. In fig. 5, the needle m n is attracted by the poles NS NS= NS; the needle o p by the poles NS NS
NS; the needle q r by the poles NS NS=NS. The needle, therefore, preserves its direction constantly the same, around the periphery of the polygon; this would happen precisely the same upon all the points of a polygon of an infinite number of sides, or in the circle, as in fig. 6, so that there will be an appearance of the needle being directed by a current around the periphery in the same direction.
8. A superposition, or continuation of endless magnets, constitutes the transverse magnet, i.e. in a transverse magnet every section perpendicular to its axis is an endless magnet. The transverse magnet presents no poles at its extremities; but the heteronomous poles succeed each other alternately in the periphery of these sections. I have shown in a memoir which is inserted in the Annales de Physique already mentioned, that in forming a