The reasons for and against an essential resem blance between magnetism and electricity might, before the discovery of electromagnetism seem to be nearly balanced. The most striking analogies were, that each of them consists of two powers, or directions of powers, of an opposite nature, sub mitted to the same laws of attraction and repulsion; that the magnetical action on bodies, fit to receive it, has much analogy with the electrical action; that the distribution of the powers in a body, which has an electrical charge, and still more a series of bodies charged by cascade, differs very little from the distribution of the powers in a magnet; if we imagine a Voltaic pile, and principally the modifi cation denominated after Zamboni, composed of minute and molecular elements, it would have the most perfect analogy with a magnet; and lastly, that the tourmaline differs but little from such an electrical magnet.
We shall not here consider that most of these analogies are overturned by the discovery of elec tromagnetism; but still confining ourselves to the period before this discovery, it may be objected that the magnetical and electrical powers do not act on each other, which should be the case, if they were of the same nature; that all bodies transmit with ease the magnetical action, but not the electri cal; that neither the tourmaline nor any system of charged glass-plates, or of galvanical arrangements, has the effects of the magnet. Although it might be answered that the galvanical circuit, in its first period, seemed no less different from any electrical apparatus than the Voltaic pile from a magnet, these objections did not cease to have considerable weight, but we have hitherto deliberately omitted one of the arguments, viz. the observation of mag netism in bodies struck by lightning, and the ex periments made to imitate this effect. It had often been observed, that the magnetical needles in a ship struck by lightning have suffered a change in their polarity.
A very remarkable case of this kind, mentioned in the Philosophical Transactions, Vol. xi. No. 127, p. 647, seems to be the earliest on record. It is there related that a vessel, whose mast was struck by lightning, had the poles of the needles in all its compasses inverted, yet the compasses them selves were not struck. Some other observations of a similar nature are recorded in Domsdorph's Treatise upon Electricity, Magnetism, Tire, and Ether, (uber Electricitat, Magnetismus, Feuer and Ether, 1783.) An accident of this kind, which happened in the year 1751, caused Franklin to try the effect of artificial electricity upon needles of steel. The result was, that when the needles were in a position in which the earth could produce in them some magnetism, this effect was much in creased by any electrical stroke; but when the po sition gave no such advantage, he found that the extremity of the needle, in which the electricity en tered (which received the positive electricity) was directed towards the north, when the needle was conveniently suspended. Trilelee, who repeated these experiments, obtained the same results, only with the difference, that in the case when the direc tion of the electrical stroke seemed to decide the polarity, this was the inverse of that observed by Franklin. (Transactions of the Royal Academy at Stockholm, 1766.) The experiments made in the
year 1785, upon the same subject by van Marum and van Swinden have been considered as decisive against the magnetical effects of electricity, never theless the ninth of their experiments was precisely an electromagnetical one, for they led the electrical discharge transversely through a steel needle, and obtained a strong magnetical polarity in a direction perpendicular to the magnetical meridian; but they considered this as a singularity not to be explain ed, and hence it has been out of the sight of philo sophers from the year 1785 until 1820, when elec tromagnetism was discovered. (See ran Marurn, description d'une t•s granite machine electrique.) One of the earlier experiments, which probably belongs to electromagnetism, is that of Cavallo, by which he proved that iron has more efficacy on the rnagnetical needle, when an acid,particularly dilut ed sulphuric acid, acts upon it.
Joh. Win. Ritter, already mentioned, pursued a great number of researches upon the analogy of magnetism and electricity. lie had in the year 1801 made a series of very delicate experiments upon the galvanical difference between the two magnetical poles of a steel needle. The result de duced from his experiments was, that the southern extremity of the needle was more oxidable than the northern, and that the galvanical effect of two magnetical needles upon a. frog was such, that the south pole acted as the more oxidable, the north pole as the less oxidable metal. It is now acknow ledged, that he has been led into error by the dif ference which a small disparity in the polish of the metal can produce, and which he employed insuffi cient means to avoid. The same philosopher stated likewise erroneously, that a platina wire, which has been employed to make a liquid communicate with a powerful galvanic circuit, assumes some magnetical direction, and that a needle, of which one half is zinc and the other silver, takes, when conveniently suspended, the same direction as the magnetical needle. The precipitation with which Ritter published these and some other erroneous statements, has thrown a shade over the name of this unhappy but ingenious philosopher, who has enriched science with several discoveries of great importance, and whose profound yet obscure ideas in many cases have anticipated the discoveries of future times. We are far from patronizing a vain exhibition of new ideas, by which it is possible for a very ordinary mind to make pretensions to every new discovery; but when works are marked with the true stamp of genius, it is but justice to ac knowledge the merits of their speculations. Some writers have thought that this act of justice would deprive experimental philosophers of a part of the honour due to their exertions; but this honour is quite unimpaired, if the author, who has anticipat-' ed their discoveries, has only had a vague and ob scure notion of them; while it must be avowed, that when the author has clearly announced the dis covery, has derived it from good data and conceiv ed its connections with other truths, the merit of the experimental philosopher is-only that of having confirmed it by experiment, which still in many cases can be a work of no smaller claim to glory than the primitive conception itself.