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قراءة كتاب The Earliest Electromagnetic Instruments
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the Society a bow-pattern of multiple-wound, wax-insulated wire, Figure 3. [There were no illustrations with Schweigger’s first paper.] While a single wire, using the weak electric circuit here, deflects the magnetic needle only 30° or 40°, if the compass is placed in one of the openings of this pattern, the needle is deflected 90° to the east, or in the other opening 90° to the west, using the same weak electric circuit....
The “bow-pattern” device has novelty interest only, adding nothing to the elucidation of the multiplier phenomenon. The same is true of Schweigger’s next proposal, shown in figure 4. “... I will now add another apparatus, which is just an extension of the previous one, whereby the needle can take up any angle from 0° to 180°.” A short length of circular glass tubing, of inside diameter large enough to contain a compass needle, stands with its axis vertical and has single or multiple loops of wire wound on it in vertical diametral planes. In the illustration, successive plane coils are inclined at 30° to one another. “... the electric current flows through the whole wire, and the needle moves under all of these currents, and coming always into another loop can take any desired angle.”
With much further theorizing about “the correlation of magnetism with the cohesion of bodies,” Schweigger states again his evaluation of his discovery: “Oersted succeeded in electromagnetic research by using a spark-producing cell, which could make a wire glow. My amplifying electromagnetic device needs only a weak circuit of copper, zinc, and ammonium chloride solution.”[24]
Figure 4.—Schweigger made this peculiar construction of wire coils, wound endwise on a short vertical section of glass tubing with a compass needle inside, merely to startle his Halle audience with the fact that the compass needle could rest in any of several stable positions. (From Journal für Chemie und Physik.)
Figure 5.—Schweigger’s suggestion of one possible design for an amplifying electromagnetic indicator. The components are wooden rods and insulated wire. Position b referred to in the text is at the bottom of the diagram between the letters a and c. (From Journal für Chemie und Physik.)
“FURTHER WORDS ABOUT THE NEW MAGNETIC PHENOMENA”
[This was presumably written between November 4, 1820, and the January 1, 1821, publication date of his Journal.]
These wonderful new electrical effects[25] are most easily rendered perceptible with the help of the previously described wire loops. To focus attention on just one of the windings of Figure 3, we sketch a new drawing, Figure 5.... Since it is of major importance that these loops be made of silk-covered wire lying evenly on one another, it is convenient to wind the loops on two small slotted sticks of wood, although it is also possible to hold the wires together with wax or shellac, or to tie them together in an orderly manner with silk thread....
In Figure 5, Aa and Cc represent little slotted rods of wood on which the silk-covered wire is wound. Only three windings are shown in the figure, but I generally adopt three times that many. Now t is connected with the copper and d with the zinc, and the compass B set between the rods Aa and Cc with the coil perpendicular to the magnetic meridian and the terminals d, t at the east.
The instant Z and K are dipped in the ammonium chloride solution, the needle turns around and stays with the north pole point south....
If now the compass is taken out of the coil and put in position b, all effects are reversed, and are considerably weaker, for obvious reasons....
It is of the same significance whether we bring the compass from B to b in Figure 5, or from mesh 1 to mesh 2 in Figure 3, only that in the latter case, because the compass is enclosed by the two sides, a stronger effect results....
If now the coil is rotated ... so that the face previously north now faces south, then on connecting the electric circuit there is absolutely no trace of effect on the needle, assuming that the terminal wires are not reversed....
It seems unnecessary to note that our magnetic coil can be placed in the direction of the magnetic meridian or at any arbitrary angle with it....
Following several pages of further talk about the relation of “cohesion to magnetism” and about “unipolar and bipolar conductors,” the only additional item of interest is the observation that discharges of a Leyden jar (Kleistichen Flasche) strong enough to burn strips of leaf gold and to magnetize an iron rod in a coil, produced no compass-needle deflections, even with the help of the “amplifying apparatus.”
Schweigger, therefore, described the basic multiplier idea clearly enough in his first paper, but offered no sketch of the simplest construction until the third paper. In the second paper, meanwhile, he had illustrated two peculiar designs involving the principle in less elementary ways.
His indifference to whether the wire loops lie in the magnetic meridian (fig. 3) or perpendicular to it (fig. 5) or “at any other arbitrary angle to it,” reveals a poor appreciation of the measuring-instrument potentialities. His conception seems to be primarily that of a detector.
Poggendorf’s invention, as first reported by Erman and presented to a wider audience by Gilbert[26] was described as consisting of typically 40 to 50 turns of 1/10-line diameter, silk-covered copper wire tied tightly together, with the whole pressed laterally to form an elliptical opening in which a pivoted compass needle could move freely while maintaining clearance of about 2 lines from the wire at all points.[27]
“This magnetic condenser can be a great boon to electro-chemistry,” said Erman, for “it avoids all the difficulties of electric condensers.” He noted that, using the condenser, Poggendorf had already established the electric series for a great number of bodies, discovered various anomalies about conductivities, and found a way of detecting dissymmetry of the poles of a compass needle. On the other hand, even with the condenser, no magnetic effects have so far been obtainable from a strong tourmaline, or from a 12,000-pair, Zamboni dry cell.
Poggendorf’s own account of his work finally appeared as a very long article in the journal known as “Oken’s Isis.”[28] The editorial controversies mentioned earlier may have occasioned this use of a