cerning this mysterious kind of attraction has been greatly augmented. The points in which it resembles, and those in which it differs from electricity, have been more satisfactorily ascertained; and a nearer approach made than formerly to a systematic arrangement of the magnetic laws.

The unexpected and daring introduction of mathematical principles and demonstration into the dark regions of electricity, by Mr. EPINUS, was mentioned, in a former page, as one of the signal improvements of the last century. This ingenious philosopher has done the same in magnetism, and with equal success. And though this subjection of the magnetic principles to the most precise and definite of all species of investigation does not appear to have led, as yet, to any extraordinary discoveries, or radical reforms in theory; yet it has been by no means without its use, and may conduct to invaluable acquisitions.

The Mariner's Compass, within the period in question, has been considerably improved. This important instrument, after its invention in 1302, long remained in a rude and imperfect state. But Dr. KNIGHT's discovery of the mode of making ar tificial magnets, about the year 1744, together with the results of some other experiments, enabled him to render the compass much more convenient and useful. To his improvements may be added the further emendations of Mr. SMEATON, and Mr. M'CULLOCH, both of Great-Britain.

The variation of the magnetic needle has been a subject of much attention and of much ingenious speculation, during the past century. The observations made by Dr. HALLEY, and published in 1701, in the form of a variation chart, were of

See Tentamen Theoria Magn. et Electr. Petrop. 1759. See also the Supplement to the American Encyclopædia, by Dobson, articles Electricity and Magnetism,

F

great use to navigators, and contributed not a lit tle toward reducing the principles of this variation to something like an intelligible form. The next. attempt of the same kind; worthy of notice, was. that of EULER. This philosopher, equally remarkable for the extent of his learning, and the vigour and comprehensiveness of his mind, undertook, about the middle of the century, to account for the magnetic irregularities, and to ascertain, the position of the needle in every part of the earth. He executed his task with singular ingenuity and perseverance; and with a plausible appearance of success. But his theory, and the whole structure founded upon it, were soon found liable to such objections, that they were considered of little value, excepting so far as they might furnish a guide in the further prosecution of the inquiry. Since the time of EULER, many others have exerted their genius in the same investigation; but without producing more certainty or satisfaction. Among the latest explorers of this dark but important subject, Mr. CHURCHMAN, a respectable citizen of our own country, deserves to be honourably mentioned. He has, in his own opinion, made valuable improvements on the theories of HALLEY and of EULER; corrected various errors into which those great philosophers fell; and given an hypothesis which bids fair to be of more practical utility than theirs to the nautical adventurer. How soon this hypothesis may be brought to the test of a complete course of experiments; or how it may bear this test, when subjected to it, are questions yet to be solved. In the mean time, the ingenuity, zeal and perseverance, evinced in Mr. CHURCHMAN's late publications on this subject, de serve the attention, the thanks, and the encouragement of the philosophic world."

See Churchman's Magnetic Atlas, 4to. 3d edition 1800

Many other writers, of acknowledged scientific eminence, have distinguished themselves by new experiments, and ingenious hypotheses on magnetic attraction, within the period of which we are speaking. Among these may be mentioned MUSCHENBROECK, WHISTON, CELSIUS," VAN SWINDEN, LAMBERT," EULER," KNIGHT, MITCHEL, CANTON and CAVALLO. To detail the opinions entertained, and the facts successively brought to light by each, would far exceed our prescribed limits. But, after all the inquiries of these philosophers, it must be acknowledged that "clouds and darkness rest" upon this part of science; that even its general principles are little understood; and that we are yet far from being furnished with materials for a satisfactory system on the subject. Perhaps another century may accomplish this, which, when viewed in its various relations, must be regarded as a grand desideratum in philosophy.

In 1774 arose the idea of a certain sympathy existing between the magnet and the human body, by means of which the former might be applied to the cure of diseases. This opinion appears to have originated with Father HEHL, of Germany, who greatly recommended the use of the magnet in medicine. On some experiments and suggestions of HEHL, the famous MESSMER, a German physician, about the year 1766, erected his fanciful system of Animal Magnetism. The noise

+ Dissert. Physico Experimentalis de Magnete.

u Tentamina Magnetica, 4to. Also Memoirs on the Analogy between Elect. and Mag. 3 vols. 8vo. 1785.

The experiments and calculations of M. LAMBERT, on the polarity and variations of the magnetic needle, deserve particular attention. He was a most accurate and sagacious philosopher. See the Memoirs of the Academy of Berlin, for 1756, published in 1758.

w Euleri Opuscula. tom. iii. Continens Theoriam Magnetis, Berlin, 1751. x An Attempt to explain the Phenomena of Nature by Two Principles, e. 4to. 1748.

made by the opinions and arts of this celebrated empiric, and his coadjutors, in Germany, in France, and indeed, though in a less degree, throughout every other part of Europe, is well known to all acquainted with the literary history of that period; as well as the detection, the decline, and the final disgrace of them, and their principles."

MOTION, AND MOVING FORCES.

This part of science also, within the century under consideration, has received no small improvement. The laws of motion, as laid down by Sir ISAAC NEWTON, though found, by succeeding philosophers, to be in general correct, were yet by no means perfectly so. His principles of motion in resisting mediums, particularly failed, when brought to the test of accurate experiment. Numerous have been the attempts to supply the defects, and to correct the errors of these principles: among which the labours of D. BERNOULLI, and of M. D'ALEMBERT, deserve to be considered as by far the most distinguished and successful. The latter in particular, in the course of his investigations, discovered a general rule, adequate to the determination of many important questions in the science of motion, and applying to the most compound and perplexing cases."

The inaccuracy of NEWTON's principles, with regard to projectiles, was first ascertained and announced by M. RESSONS, a French artillerist, in 1716. Nothing material, however, was done toward the establishment of new and more just laws, till 1742, when BENJAMIN ROBINS, of Great-Britain, published his New Principles of Gunnery, a

y For an amusing account of the noise and pretensions made by MESSMER, see WILLICH's Lectures on Diet and Regimen, &c. p. 106, &c. New-York edition.

Z CONDORCET on the Mind, p. 275.

very able work on the subject of projectiles, which threw much new light on this part of philosophy, and advanced a theory much nearer to perfect accuracy than had ever been given before. ROBINS was followed by his countryman Mr. C, HUTTON, who contributed to a further elucidation of the subject by a number of new and interesting experiments. After him, Mr. BENJAMIN THOMPSON, and Mr. LOVELL EDGEWORTH," corrected some of the errors into which ROBINS had fallen, and considerably extended and improved his theory. In addition to the inquiries of these British Philosophers, several ingenious men on the continent of Europe contributed to the extension and confirmation of ROBINS's theory. Of this list M. D'ANTONI, of Italy, and Messrs. D'ARCY, and LE ROY, of France, are entitled to particular distinction.* Besides these, many experiments have been made, and valuable ideas suggested, respecting motion in resisting mediums, by GRAVESANDE, by J. BERNOULLI, by EULER, by SIMPSON, by M. BOUGuer, and by M. CONDORCET, Abbé BossUT, Chevaliers BUAT and BORDA, and other members of the Royal Academy of Sciences at Paris. And although this part of mechanical philosophy can scarcely be said yet to have received satisfactory elucidation; still much has been done toward the attainment of this object by the mathematicians and artists of the last age; and especially by those of France, who, in the various parts of science immediately subservient to the business of the Engineer, have certainly, in modern times, exceeded all the rest of the world.

The discoveries and improvements made, in the course of the last century, with respect to the con

a Philosophical Transactions, vols. 71 and 73, and GLENIE's History of Gunnery.

6 HUTTON'S Mathematical Dictionary.