John T. Stock University of Connecticut Storrs, 06268
James Cumming: A Pioneer in Electrical Instrumentation
Sometime during the period winter 1819-spring 1820, Hans Christian Oersted (1777-1851) noted that a compass needle was deflected when a wire carrying an electric current was brought to suitable proximity ( I ) . News of this discovery travelled raoidlv and triaaered widesoread hut independent research i n t i electromagnetic effects. Before the end of 1820, Ampere had begun to publish the series of papers which are the basis of our understanding of such effects (2). In the same year, Arago described the temporary magnetization of iron by use of an electric current (3) and, later on ( 4 ) .the phenomenon now utilized for the "maanetic damping" of moving conductors. For a feeble current, the Oersted single-wire arrangement produces only a small effect. With our advantages of hindsight, it seems obvious that the effect might he magnified if the current had to pass through a succession of suitably placed "single wires." The wires cannot be arranged end-to-end in zigzag fashion all above or all below the needle, because the repeated reversals of the direction of current flow nullify the deflecting effect. However, Oersted himself had noted that the direction of deflection reverses if the current-carrying wire is moved from above the needle to below it. Thus, the deflecting force should be augmented if the wire passes over the needle and then back under it. This is essentially a single-turn coil. For a given current, the deflectina force should be even greater with a multioleturn coil. ~ l t h o u ~ the h absolute priority appears to heiong to Johann Salamo Christuph Schweigger (1779-18571, Professor of Chemistry a t Halle, both he and Johann Christian Poggendorf (1796-18771, then a student and later Professor a t the University of Berlin, independently introduced the multiple-turn deflecting coil during the period late 1820 to early 1821 (5). The idea is so simple that it must have occurred quite independently to other scientists. One to whom it certainly occurred very early was James Cumming (1777-1861), Professor of Chemistry a t Cambridge (Fig. 1). According to Bettany ( 6 ) , Oersted's experiments were included in the lectures given by Cumming in 1819. Cumming began to read the account of his investigations to the Cambridge Philosoohical Societv on Aoril 2. 1821 (7). He continued his lect&e a t the meeting hkld on the 21st of the following month (8). The account of the April 2 address contains the statement "As your Council have-done me the honor of desiring me to repeat these experiments before you . . . ." It therefore seems unlikely that Cumming was describing work that he had just carried out. His experiments may even predate those of Schweigger and of Poggendorf. The April address, "On the Connexion of Galvanism and Magnetism," is concerned largely with Cumming's extensions of Oersted's experiments. In Cumming's day, the nature of an electric current was of course a matter of sneculation. The flow could be unidirectional, or might consist of streams of "oositive" and "neeative" electricitv that travel thrm~ghthe wire in opposite d ~ r e c t ~ mCumming s. reasoned [hat, ~f the current is imidirectional. the "narricles" musr attract one pole of the magnetic needle andiepel the other. If the flow is a dual one, then the situation is that of ". . . the one acting upon one pole of the needle solely, the other on the other." Cumming experimented with a compass needle that had one end of steel, the other of brass. Placing an
Figure 1. James Cumming (reproduced by permission of the Master and lows of Trinity College, Cambridge).
Fel-
"East-to-West" wire over this composite needle, he found that it did not move when the East end of the wire went to the zinc plate of his zinc-copper battery or cell. When the battery connections were interchanged, "the poles of the needle were reversed." In Cumming's words And therefore the effects of the connecting wire upon the compass needle are precisely similar to what would have been produced by placing over it a magnetic bar at right angles to the connecting wire, that is parallel to the needle; having in the first case, its poles in the opposite, and in the second case, in the same direction as those of the compass needle. Using a single zinc-copper cell as source, Cumming experimented with wires of different diameters, each of which was placed a fixed distance from the compass needle. He found that the deflection of the needle increased with wire diameter until the diameter was larger than %o in. Had he extended his experiments with finer wires, Cumming might have foreshadowed the conclusions reached by Ohm some five years later (9).Failure to obtain a larger deflection by use of a wire of larger diameter is of course due to such factors as polarization of the electrodes and the increased influence of the internal resistance of the cell. Cumming seemed to be feeling in the right direction, because he exverimented with a cell with a movable zinc nlate. He found that, as this plate was brought nearer to t i e copper plate, the deflection of the needle was increased. Figure 2 is reproduced from the plate that is interlaced between the accounts of the two parts of the lecture (7, 8). The use of "galvanometer" and "galvanoscope" indicates that Cumming proposed to measure, as well as to detect, electric currents. The term "galvanometer" had been ap~~
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plied to a purely electrostatic device some 20 years earlier (10). The first use in connection with an electric current was hv Amnere in 1820 (11). Cummine's wlvanoscone is intereking 'in showing t h a t he had cieariy grasped the "multi-turn" nrincinle. His ealvanometer involves vet another fundamental'idea. H; realized that the sensitivity could be increased hy reducing the deflection-opposing effect of the earth's magnetic field. T o bring this about, he suitably located a small "neutralizing" magnet beneath the compass needle. In 1823. Cumming described a "neutralization" arrangement that permitte;i easy adjustment (12). This is the ancestor of the "control magnet" system, much used in highsensitivity moving-magnet gal;anometers developed -by later workers. T o illustrate the sensitivity attainable, Cummine connected a silver and a nlatinum wire to the resnectiveends of the galvanoscope coil and then twisted the't'ree ends of there wires toeether. When the twist was heated bv a spirit lamp, the neidle deflected through a large angle. The source of electricity here is the thermoelectric effect. This effect is often named for Thomas Johann Seebeck (1770-1831) (13.14). In his "Rede Lecture on Thermoelectricity," ~ a i t ( l 5 points ) out that Cumming seems to have made an indenendent discoverv of the thermoelectric effect. cummini used his galvan&ope to study this effect and read an account of his findings a t a meeting of the Cambridge Philosophical Society in April, 1823 (16, 17). Some years later, he gave a report on thermoelectricity to the British Association for the Advancement of Science (18). In Cumming's galvanometer (Fig. 2(a)), the currentcarrying, or "connecting," wire AB is mounted on a slide that travels alongside a vertical scale. The distance between the wire and the compass needle can therefore be varied a t will. Cumming (8)". . . found that the tangent of the deviation varies inversely as the distance of the con-
necting wire from the magnetic needle." However, he favored measurement of the distance required to produce a standard anele of deflection. This method enabled him to use a smallerand more delicate compass needle. Experimenting with various electrolvtes in a small zinccoppir cell, ~ u k m i n gfound that phosbhoric or acetic acid was much less effective than hvdriodic or oxalic acid. When he used strong sulfuric acid, the needle scarcely moved ". . . but on adding a drop of water, it deviated through more than half a right angle." This is an early but striking demonstration of the ionizing properties of water. The modernday interest in alkali-metal power batteries has some ancestry in Cumming's work. In experiments with cells other than the co~oer-zinc varietv. .. .. he tried the combination ootassium-zinc. ". . . the Potassium took fire before I could observe the effect: this difficultv - I afterwards obviated bv alloying it with mercury.. . ." Althoueh of Scottish ancestrv. Cummine was born in England ( 6 ) P ~ eentered Trinity &llege, cambridge, in 1797, became Fellow in 1803, and was elected Professor of Chemistry in 1815. An excellent teacher, he continued t o lecture until 1860. then continued lahoratorv work until a few weeks of his death in the following yea; Apart from his galvanometric and thermoelectric work. he left brief descrivtions of an ether-distillation device for measuring the heat of the sun's ravs and of a thermometer for assessing- the heating effect df an electric current (19). The "Manual" (Fie. 3). based on J. F. Demonfarrand's "Manuel d'J31ectricit.i ~ G a m i ~ u e ,is" Cumming's longest scientific work (20). This book is far more than a mere translation; the "notes and additions" are considerable. The copy in the Library of the University of Glasgow was given by Professor James Thomson (Lord Kelvin's father) to Robert Thomson. The recipient was probably Kelvin's younger brother (21). Apparently, Cumming's health was uncertain, and this may have limited his ambition. However, his work on galvanometry alone gives him an honored place in the history of the development of scientific instruments. Literature Cited (1) Dibner, B., "Oorrfcd and the Dismven, of Eloetromagnctiam."Blaisdell Publishing Co.. New Vork, 1962. p. 25. (2) Appleyard. R., "Pioneers of Elee~iealCommunication:' MscMillan. London, 1930.
MANUAL 0.
ELECTRO DYNAMICS,
Figure 2. Apparatus described by Cumming (for dariiy, the item numbering on the plate has been changed lo lower-case lellering, but the descriptions are as given by Cumming). (a) The Galvanometer. AB, Me connecting wire placed over Me compass needle SN. AC. BD, tubes filled with mercury for forming the connection with the positive and negative ends of the batlery. and snached to the slide EFGH. (b) The Galvanosmp. A. K, tubes filled wilh mercury, to be connected with the Galvanic plates. ABCDEFGHK, a wire passing in a spiral round the compass needle NS. A small magnetized needle is placed beneath NS to neutralize the terrestrial magnetism. (c)and (d) Two forms of spirals f w increasing the eiectm-magnetic intensity.
30 1 Journal of Chemical Education
BY JAM&. CUMMISG, M.A. F.US. B c..,,
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Amgo. F. J..Ann. Chim. Phys., 15.93 (1820). Bahhage. C.. and Herschel, J. F. W., Phil Trans. Roy. Soc., 115,467 (18251. Chipman. R. A.. Smithamion lnrlilulion Bullatin, No. 240, p. 127 (1965). Bettany, G.T.. in "bietionsry af National Biography: 1Editors: Suphen. L.. and Lee. S.). Oxlord Uni&ity Pre86. 1888 D D W B ~ ~ PVet. . 5, p. 296. Curnrning. J., T r a m CombridsePha Soc.. 1.269 11822). Cumming, J., Tmns. Combrid~ePhil.Sor., 1.281 118221. Heathcote, N. H. deV..Sri. Progress 26, No. lOl.51 (1931.32). Whipple, R. S.,J Sci. Instrum.. 11.37 (1934). Ampire. A.M., Ann. Chim. Phys., 15, 59 11820). Cumming. J.. Thornson's Ann. Phil.. 22.288 1~8231. Sesbeek.T. J..Abh. Ahad Wiss Berlin. 239, 11822-231.
1141 Soebeck,T.J..Ann. Phys Chsm. 1PoEgendarll.6.111826l. 1131 Tait,P. G . , N d u r # , 8,8611873). I161 Cumming, J., Trans. CambridgePhil. Soc., 2.47 (18271. 1171 Cumming, J., Thamronb Ann Phil.. 21.427 11823). 118) Curnming, J., Report of the 2nd Meeting Brit. h o e . Advance. Sei.. 1832. John Murray, London, 1833. p. 301. 119) Cumming, J., Report of the 3rd Meeting, Brit. Assoc. AdvanceSci.. 1833, John Murray, London. 1834. p. 418. IM) Cumming, J.. "A Manual of Electm Dynamics: Deighton, J., and Deighton, d. J.. Cnmhr?dve --., tR27~ (211 Lloyd, J.T.. wrsonalcornmunication, April 14. 1972. ~~~
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