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 pre- 

 viously 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 "•uni- 

 polar 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 prin- 

 ciple 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. 



Poggendorfs 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 

 }i -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 i ould move freely while maintaining clearance 

 of about '2 lines from the wire at all points.- 7 



"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 estab- 

 lished the electric series for a great number of bodies, 

 discovered various anomalies about conductivities, 

 .mil found a wa\ 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. 



Poggendorfs own account of his work finally 

 appeared as a very long article in the journal known 

 as "Oken's Isis." 28 The editorial controversies men- 

 tioned earlier may have occasioned this use of a 

 periodical of such minor status in the fields of physics 

 and chemistry. 



The source of Poggendorfs vision of the multiplier 

 principle was a little different from Schweigger's 

 inspiration. Aiming at some detailed analysis of 

 Oersted's observation, Poggendorf ran the connect- 

 ing wire of his cell-circuit along a vertical line to just 

 above or below the pivot-point of the compass needle, 

 then, after a right-angle bend, horizontally above or 

 below one of the poles of the needle. As he studied 

 the deflections produced for all four possible positions 

 of such a wire, with both cell polarities, he came to 

 realize that if a tectangular wire loop in a vertical 

 plane enclosed a compass needle, all parts of the 

 horizontal sides of the loop would produce additive 

 deflections. By a separate experiment, he showed 

 that the vertical sides of the loop would also increase 

 the deflections. He saw at the same time that the 

 effect of additional turns would be cumulative. 



The multiple surrounding of the needle by a silk- 

 covered wire, in a plane perpendicular to the long axis 

 of the needle, affords the physicist a very simple and 

 sensitive means of detecting the slightest trace of gal- 

 vanism, or of magnetism produced by it, so that I have 

 given the name of magnetic condenser to this construc- 

 tion, though I attach no special value to this name .... 



In analyzing the astonishingly increased power which 

 the condenser gives to the magnetic effect of a circuit, 

 the first question that arises is how the effect varies 

 with the number of turns, whether it increases indefi- 

 nitely or reaches a maximum beyond which additional 

 turns have no effect. The answer to this first question 

 is linked to the solution of another, viz, whether the 

 degrees deflection are a direct expression of the measure 

 of the magnetic force or not. 



To instruct myself on this point I made use of three 

 separate circuits, each containing an 8-turn condenser, 

 and put these as close together as possible in the magnetic 



( )p. (it. (footnote 19), pp. 422-426. 



: i in.- "line" seems to have been about ' j ■ inch. 



"J. G. Poggendorf, "Physiscli-chciiiischc Untersuchungen 

 zur naheren Kenntniss des Magnetismus der voltaischen 

 Saule," Isis von Oken (1821), vol. 8, pp. 687 710. Most of 

 Poggendorfs numerical data is also in C. II. Pi am, Det 

 Elektromagntlismui (Hamburg, 1824), along with some of 

 I'l.ill 's own work. 



132 



P.I III UN 21(1: OONTRIH! 'TIONS FROM I HP Ml SKIM OF HISTORY AM) IT.CHNOI.OOY 



