Adding some coils with fewer turns, and connecting various combinations “as a continuum” (i.e., in series), the deflections using the same cell were:

Turns15102550751002003004005006007008009001000
Deflection in degrees1022273035-404040404040414040404040

Making a few coils from wire with 1/8-line diameter, the deflections, again using the same cell were:

Turns52550100Over 100
Deflection in degrees20-2240-45456565

Since the needle used in these experiments was almost as long as the inside clearance of the coils, no simple tangent law can be applied, and it is not possible to discover an equivalent circuit in modern terms. However, the constancy of the deflections for large numbers of turns in each case indicates that the cell voltage and resistance were fairly constant, and a rough estimate suggests that the cell resistance was comparable to the resistance of one of the 100-turn coils of fine wire. Such a value means that cell resistance limited the maximum deflections for the parallel-connected multipliers, while coil resistance fixed the limit in the series case.

For all of these reasons, it was impossible that any useful functional law could be obtained from the data.

Poggendorf concluded only that “the amplifying power of the condenser does not increase without limit, but has a maximum value dependent on the conditions of plate area and wire size.” He added two other significant comments derived from various observations, that the basic Oersted phenomenon is independent of the earth’s magnetism, and that the phenomenon is localized, i.e., is not affected by distant parts of the circuit.

Only a small fraction of Poggendorf’s paper is devoted to elucidating the properties of the condenser. A similar amount is concerned with refuting various proposals, such as those of Berzelius and Erman, about distributions of magnetic polarity in a conducting wire to account for Oersted’s results. More than half of the paper describes results obtained by using the condenser to compare conductivities and cell polarities under conditions where no effect had previously been detectable. Notable is the observation of needle deflections in circuits whose connecting wires are interrupted by pieces of graphite, manganese dioxide, various sulphur compounds, etc., materials which had previously been considered as insulators in galvanic circuits. Poggendorf gives these the name of “semi-conductor” (halb-Leiter).

Figure 6.—Electromagnetic instruments of James Cumming, used at Cambridge in 1821. One is a single-wire “galvanometer,” following Ampère’s definition. Cumming called the multiple-turn construction “galvanoscopes.” He showed how to increase their sensitivity by partial cancellation of the earth’s magnetism at the location of the compass needle. (From Transactions of the Cambridge Philosophical Society, vol. 1, 1821.)