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HISTORICAL SKETCH OF ELECTRO-MAGNETISM

The discovery of the identity of lightning with Electricity* called forth the wholeenergies of the electrical world, which, as if by the power of magic, were immediatelydirected to the particular branch of study occasioned by this important event; andexperiments multiplied in abundance, and from every quarter, to ratify the discoveryof Franklin. Experimenters vied with each other in imitating the splendid lightningof the heavens, by increasing the powers of their machines and augmenting the sizeand number of their jars. At length Cuthbertson brought forward his majestic doubleplate machine, the energies of which, combined with the immense Teylerian batteryof jars,-j" produced such tremendous electrical explosions as could hardly be called animitation, but lightning and thunder in reality.

Amidst this grand display of electrical refulgence, philosophers were not inattentiveto the subject of Electro-Magnetism ; and the great facilities that were afforded in theirinquiries, by the important improvements in the electrical apparatus, and the immensequantity of electrical force which could at any time be commanded, inspired hopesbordering on the certainty of success. The subject was therefore pursued with an ardourproportionate to the interest it presented by almost every Electrician of the day.

Success for a while seemed to attend the labours of those arduous experimenterswho were engaged in the pursuit, by the production of magnetic polarity in bars ofsteel submitted to electrical discharges. The electric fluid, in these experiments, wastransmitted through the bars in the direction of their length ; but the magnetic polesthus produced were soon found to have no reference whatever to the direction of theelectrical discharge: a north pole would sometimes appear at that extremity of theferruginous bar which was directed towards the positive side of the jar, and sometimesat that placed towards the negative side ; thus placing the mind of the experimenterunder the most unenviable impressions—on the one hand, hope lingering in the dis-tance, and, on the other hand, trembling on the brink of despair. Ultimately, how-ever, it was discovered that the results of all these laborious investigations had nosuperiority over those usually produced by the blow of a hammer, or other mechanicalaction, which could agitate, to a sufficient degree, the particles of the steel bars—during the trembling motions of which the polarization is facilitated by an enhancedsusceptibility of arrangement of the residentiary magnetic matter natural to the metal,whilst under the influence of terrestrial magnetic forces.

Alien a soft iron bar is placed in the position in which the dipping-needle seeks torepose, its magnetic matter becomes arranged by the influence of terrestrial magneticaction; and its polarization is similar to that of the needle, with respect to their

* Franklin formally announced his opinion of the identity of lightning and electricity, in the year 1749 ; and the firstsuccessful experiments in verification of the justness of the hypothesis were made in France, by M. d’Alibard, onthe 10th of May, 1752.

t This renowned battery was made by Mr. Cuthbertson, in the year 1786 : it consisted of 100 glass jars, each of which wascovered with five square feet of coating on each side ; so that the discharge was made from 500 square feet of coated surface.