. Bulletin - United States National Museum. Science. Figure 6.—Electromagnetic instruments of James Cumming, used at Cambridge in 1821. One is a single-wire ''; following Ampere's definition. Cumming called the multiple-turn construction "; 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.) noting that the sides of a circuit produce additive effects on a needle, he comments that a flattened rectangul
. Bulletin - United States National Museum. Science. Figure 6.—Electromagnetic instruments of James Cumming, used at Cambridge in 1821. One is a single-wire ''; following Ampere's definition. Cumming called the multiple-turn construction "; 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.) noting that the sides of a circuit produce additive effects on a needle, he comments that a flattened rectangular loop produces nearly quadruple the effect of a single wire. The paper is primarily a review of Oersted's work, with references to electro- magnetic observations before Oersted, and accounts of various related but nonmultiplier experiments that Cumming has made. His second paper, of May 21st, contains a fine plate (fig. 6) illustrating ar- rangements used in investigating the subject of the paper's title "The Application of Magnetism as a Measure of ; (Neither Poggendorf nor any of his commentators ever illustrated his "con- denser. ") Although this plate is never referred to in the paper itself, .1 nearb) "Description" gives a few comments. The two wire patterns shown are noted as simply "forms of spiral for increasing the electromagnetic ; The mounted wire loop, with enclosed compass needle and terminal mercury cups, is clearly identical in principle with the devices of Schweigger and Poggendorf, and is called a "; The largest structure illustrated does not involve the multiplying effect. It is called a "galvanometer," consistent with Ampere's definition of that word. To use it, two leads of a voltaic circuit arc inserted into the mercury cups AC and BD, and the board EFGH carrying the cups is moved vertically until some "standard" deflection is obtained on the compass
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