176 



MATHEMATICAL AND PHYSICAL SCIENCE. 



[Diss. VI. 



nal, Oersted took no immediate measures either to 

 complete or to publish his discovery. Some months 

 appear to have elapsed whilst waiting for the conve- 

 nience of a larger battery before he repeated the ex- 

 periment with the aid of Professor Esmark and other 

 friends. The battery then employed contained 20 

 twelve-inch elements, charged with water and ^ih of 

 mixed nitric and sulphuric acids. The conducting 

 wire was heated red hot, which must have rather dimi- 

 nished the effect than otherwise. The nature of the 

 wire was found to be unimportant. If positive electri- 

 city passed from north to south through a conducting 

 wire placed horizontally in the magnetic meridian, 

 then a compass needle suspended over it had its north 

 end deviated to the west ; if under it, to the east ; if 

 the needle was placed on the east side of the conduc- 

 tor, its north end was raised ; if on the west side, it 

 was depressed. Oersted further found that needles 

 of non-magnetic substances, such as brass and gum- 

 lac, were not affected, and that the electrical efficiency 

 depended on the quantity, not the intensity, of the 

 current. These experiments seem to have been made 

 in July 1820; and Oersted and his friends being now 

 , fully alive to the novelty and importance of the dis- 



co very, he circulated extensively copies of a Latin tract, 

 dated the 21st July, in which the effects of the "electric 

 conflict," as he terms the presumed combination of the 

 opposite electricities in the " conjunctive wire" upon 

 a magnet, were described. 1 In this tract we find the 

 following expressions : " The electric conflict acts 

 in a revolving manner." " It resembles a helix." 

 " The electric conflict is not confined to the conduct- 

 ing wire, but it has around it a sphere of activity of 

 considerable extent." 



(792.) The effect of this pamphlet, consisting of a few 

 Speedily pages only, was instantaneous and wonderful. The 

 bv An> P author probably counted on the opportunity of devel- 

 pere, oping his discovery at leisure, but it was seized on 

 Arago, and with such avidity, and pursued with such signal suc- 

 Davv - cess, particularly in France, that he probably gave up 

 the race of invention in despair. Ampere had already 

 communicated experiments to the Institute on the 

 18th and 26th September. Arago and Davy sepa- 

 rately, and but little later, discovered the magnetiz- 

 ing power which the voltaic conductor exerted on iron 

 filings, and the latter tried in vain the magnetizing 

 power of common or machine electricity, which, how- 

 ever, was soon after shown by Arago, who enclosed 

 steel wires in helices of copper wire, through which 

 the discharges were passed. When soft iron was 

 placed in such a helix, it was found to become a tem- 

 porary magnet of great power whilst the voltaic 

 current continued. Thus magnets of enormously 

 greater power than any previously known were con- 

 structed ; one of the first large ones was made by Pro- 

 fessor Henry of the United States. 

 (793.) But the progress of electro- magnetismas a science 



was far more indebted to Ampere, a professor at 

 Paris, than to any other philosopher. I shall, 

 therefore, introduce here some account of his dis- 

 coveries before closing what I have to say of Oer- 

 sted. 



ANDRE MARIE AMPERE was born in 1775 at Lyon. (794.) 

 He was an able mathematician, and wrote several Electro- 

 memoirs on Chances, and on the Integration of Par- ?7 namic f 

 tial Differential Equations. But with this he com- Ampere, 

 bined a taste for, and a practical acquaintance with, 

 the experimental sciences. He was a very good che- 

 mist, and showed himself particularly attentive to 

 Davy on his first visit to Paris. He was also much 

 attached to metaphysical speculation. His skill in 

 devising apparatus and in performing experiments was 

 eminently shown in his electro-magnetic researches ; 

 whilst he judiciously rendered his mathematical 

 knowledge subservient to them. In this respect he 

 had greatly the advantage of Oersted, who appears to 

 have been little acquainted with mathematics, and, 

 perhaps, in common with his metaphysical friends of 

 the German school, misapprehended their utility in 

 physical discoveries. Three different hypotheses Various 

 were speedily broached to represent mechanically opinions 

 the singular kind of force mutually exerted between ^* 

 a conductor and a magnet. The first and most ob- O f the elec 

 vious was, that this action was not a push-and-pull tro-mag- 

 force, but a force producing rotation without direct netlc force 

 attraction and repulsion, or of the nature of a couple 

 exerted between any part of an electric current, and 

 a small magnet or magnetic element. The second 

 opinion was, that an electric current may be esteemed 

 equivalent to a magnetizing force at right angles to 

 it. The third, that a magnet is composed of ele- 

 ments which act as if a closed electric circuit ex- 

 isted independently within each of them ; that is, 

 each magnetic molecule may be replaced by a small 

 conducting wire bent upon itself, in which some un- 

 failing source of electricity, like a galvanic pair, keeps 

 up, in the same direction, a constant current. 



This last hypothesis, arbitrary and improbable as (795.) 

 it may sound, was that defended by Ampere. Whilst Theory or 

 few will be disposed to regard it as a true and com- j[ P ted "! 

 plete physical picture of the condition of magnetized Ampere, 

 bodies, it seems impossible not to award to it the same 

 sort of credit which we do to Newton's " fits of easy 

 reflection and transmission" of light, when we find 

 that it not only serves to represent the more obvious 

 phenomena, but has suggested experiments absolutely 

 new, and which turned out in accordance with the 

 anticipation ; and that, finally, by the sagacity and 

 industry of its author it was made to include, by 

 merely mathematical deductions, and without any 

 complication of the hypothesis, certain experiments 

 of a very singular kind, which at first seemed inex- 

 plicable by it. I proceed to develope a little farther 

 this consideration. 





1 The exact title was, Experiment** circa e/ectum Conflictus Electrici in Acum Magneticum. 



