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]