square feet of glass will deprive a man of sensation for a time, if the head be made a part of the circuit through which the electricity moves. No inconvenience has been found from the electric shock by men of strong habits; but women of delicate constitutions have had convulsions from a violent shock. It may be observed, that the electric shock is a proof that the electric matter can pass through the substance of non-electrics, and is not universally conducted along the surfaces alone, as some have supposed.

The object of the philosopher being, in general, to collect a large quantity of electricity, by means of the surfaces of electrics, it is more usual to employ jars, and not plates. These are made of various shapes and magnitudes; but the most useful are thin cylindrical glass vessels, about four inches in diameter, and fourteen in height, coated within and without with tin-foil, which is stuck on with gum-water, paste, or wax, excepting two inches of the rim or edge, which is left bare, to prevent the communication between the coatings. About four inches from the bottom, within, is a large cork, that receives a thick wire, ending in several ramifications, which touch the inside coating; the upper end of the wire terminating with a knob, considerably above the mouth of the jar, fig. 4. When it is required to be charged, it may be held in the hand, or placed on an uninsulated table, and the knob of the wire applied to the conductor; the inside coated surface becomes possessed of the electricity of the conductor, and the external surface acquires the contrary electricity, by means of its uninsulated coating. When a jar of this kind is highly charged, it will discharge spontaneously over the uncoated surface, and seldom through the glass; whereas, when the uncoated surface is large, it is more apt to break by that means, and become useless. Yet there is no certainty that a jar, which has discharged itself over its surface, will not at another time break by a discharge through the glass, as the contrary often happens. If paper covered with tin-foil be used for the coating, with the paper next the glass, the jar will be less liable to break.

A jar of considerable thickness, with a neck like a bottle, in which is cemented a thick tube to receive the wire, will sustain a very high charge, and produce much greater effects than one of the last description. The charging wire being inserted loosely into the tube will fall out on inverting the jar, and the charge will remain for several weeks without much VOL. VII.

loss. A jar thus charged may be put into the pocket, and applied to many purposes that the common jar cannot be used for.

If the inside of the jar be considerably damped, by blowing into it, through a tube reaching to the bottom, it will take a charge nearly one-third greater than in the ordinary state.

When a greater degree of electric force is required, larger jars must be used, in which the form is of no consequence, except as far as relates to convenience. But it is less expensive, and nearly as effectual, to use a number of smaller jars, having the same quantity of coated surface as the large jars. In this case, a communication must be formed between all the outside coatings, which may be done by placing them on a stand of metal; and also between all the inner coatings, which is best done by means of wires. Such a collection is called a battery, and may be charged and discharged like a single jar, fig. 5.

In discharging electrical jars, the electricity goes in the greatest quantity through the best conductors, and by the shortest course. Thus, if a chain and a wire, communicating with the outer coating, be presented to the knob of a jar, the greater part of the charge will pass by the wire, and very little by the chain, which is a worse conductor, by reason of its discontinuation at every link. When the discharge is made by the chain only, sparks are seen at every link, which is a proof that they are not in contact; and as the chain must be stretched by a considerable force before the sparks cease to appear on the discharge, it follows, that there is a repulsive power in bodies, by which they are prevented from coming into contact, unless by means of a certain force.

By accurate experiments, it appears that the force of the electric shock is weakened, that is, its effects are diminished by using a conductor of great length in making the discharge. Dr. Watson, and other gentlemen of eminence in the philosophical world, were at the pains of making experiments of the same kind, but much more accurate. They found, by means of wire insulated on baked wood, that the electric shock was transmitted instantaneously through the length of 12,276 feet.

When any animal or substance is to be subjected to the shock, it is done by means of two chains, one of which connects one extremity of the animal or substance with the outer coating, and the

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which was, the opening a passage from Greenland to the South Sea by the north pole. That such a passage might be found, he was so fully persuaded, that he used to say, if his situation could admit of such adventures, he would undertake the voyage, even at his own charge. But when schemes of finding it were laid before the parliament in 1741, and he was consulted by several persons of high rank concerning them, and before he could finish the memorial he proposed to send, the premium was limited to the discovery of a north-west passage; and he used to regret that the word west was inserted, because he thought that passage, if at all to be found, must not lie far from the pole.

In 1745, having been very active in fortifying the city of Edinburgh against the rebel army, he was obliged to fly from thence into England, where he was invited by Dr. Herring, Archbishop of York, to reside with him during his stay in this country. In this expedition, however, being exposed to cold and hardships, and naturally of a weak and tender constitution, which had been much more enfeebled by close application to study, he laid the foundation of an illness, which put an end to his life in June, 1746, at forty-eight years of age, leaving his widow with two sons and three daughters.

Mr. Maclaurin was a very good, as well as a very great man, and worthy of love as well as admiration. His peculiar merit as a philosopher was, that all his studies were accommodated to general utility; and we find, in many places of his works, an application, even of the most abstruse theories, to the perfecting of mechanical arts. For the same purpose he had resolved to compose a course of practical mathematics, and to rescue several useful branches of the science from the ill treatment they often met with in less skilful hands. These intentions, however, were prevented by his death; unless we may reckon, as a part of his intended work, the translation of Dr. David Gregory's Practical Geometry, which he revised, and published, with additions, in 1745.

In his life-time, however, he had frequent opportunities of serving his friends and his country by his great skill. Whatever difficulty occurred concerning the constructing or perfecting of machines, the working of mines, the improving of manufactures, the conveying of water, or the execution of any public work, he was

always ready to resolve it. He was employed to terminate some disputes of consequence that had arisen at Glasgow, concerning the gauging of vessels; and for that purpose presented to the commis. sioners of the excise two elaborate memorials, with their demonstrations, containing rules by which the officers now act. He made also calculations relating to the provision, now established by law, for the children and widows of the Scotch clergy, and of the professors in the universities, entitling them to certain annuities and sums, upon the voluntary an nual payment of a certain sum by the incumbent In contriving and adjusting this wise and useful scheme, he be stowed a great deal of labour, and contributed not a little towards bringing it to perfection.

Of his works, we have mentioned his "Geometria Organica," in which he treats of the description of curve lines by continued motion; as also of his piece which gained the prize of the Royal Academy of Sciences in 1724. In 1740, he likewise shared the prize of the same academy with the celebrated D. Bernoulli and Euler, for resolving the problem relating to the motion of the tides from the theory of gravity, a question which had been given out the former year without receiv ing any solution. He had only ten days to draw this paper up in, and could not find leisure to transcribe a fair copy; so that the Paris edition of it is incorrect. He afterwards revised the whole, and inserted it in his treatise of fluxions; as he did also the substance of the former piece. These, with the treatise of fluxions, and the pieces printed in the Medical Essays, and the Philos. Trans. a list of which is given above, are all the writings which our author lived to publish.

Since his death, however, two more volumes have appeared; his algebra, and his account of Sir Isaac Newton's philosophical discoveries. The algebra, though not finished by himself, is yet allowed to be excellent in its kind, containing, within amoderate compass, a complete elementary treatise of that science, as far as it has hitherto been carried; besides some neat analytical papers on curve lines. His account of Newton's philosophy was occasioned in the following manner. Sir Isaac dying in the beginning of 1728, his nephew, Mr. Conduitt, proposed to pub. lish an account of his life, and desired Mr. Maclaurin's assistance. The latter, out of gratitude to his great benefactor, cheerfully undertook, and soon finished, the

history of the progress which philosophy had made before Newton's time; and this was the first draught of the work in hand; which, not going forward on account of Mr. Conduitt's death, was returned to Mr. Maclaurin. To this he afterwards made great additions, and left it in the state in which it now appears. His main design seems to have been, to explain only those parts of Newton's philo sophy which have been controverted; and this is supposed to be the reason why his grand discoveries concerning light and colours are but transiently and generally touched upon; for it is known, that whenever the experiments on which his doctrine of light and colours is founded had been repeated with due care, this doctrine had not been contested; while his accounting for the celestial motions, and the other great appearances of nature, from gravity, had been misunderstood, and even attempted to be ridiculed.

MACQUER (JOSEPH), in biography, an eminent chemist, was born at Paris in 1710. He was brought up to physic, and became a doctor of the faculty of medicine in the university of Paris, professor of pharmacy, and censor royal. He was also a member of the academies of sciences of Turin, Stockholm, and Paris, and he held the medical and chemical departments, in the Journal des Savans. M. Macquer made himself well known by several useful and popular works on chemistry, of which science he was one of the most successful cultivators on the modern rational plan, before the new modelling which it has received of late years. His publications were, "Elemens de Chymie Pratique," two vols. 12 mo. 1751-1756. "Plan d'un Cours de Chymie experimentale et raisonnée," 12mo. 1757. This was drawn up in conjunction with M. Baumé, who lectured on chemistry in partnership with him; "Dictionnaire de Chymie," two vols. 8vo. 1766. These works have been translated into English and German: the dictionary, particularly, by Mr. Keir, with great additions and improvements. He wrote likewise "Formulæ Medicamentorum Magistralium," 1763; and "L'Art de la Teinture de Soie," 1763; and he had a share in the "Pharmacopeia Parisiensis," of 1758. This meritorious writer died in 1784. Dict. Hist. de la Med. par Eloy. Nouv.

one-valved, three jointed, and furnished with three bristles; antennæ projecting, very short, submoniliform, clavate; head oblong, cylindrical above; scutel as long as the abdomen, depressed, membranace. ous. There is only one species, viz. M. cimicoides, found in North America; the body is a ferruginous grey; scutel pale ash with a yellow rigid spot; underwings purplish violet; fore-shanks thickened.

MACROCNEMUM, in botany, a genus of the Pentandria Monogynia class and order. Natural order of Contorta. Rubiacea, Jussieu. Essential character: corolla bell-shaped; capsule two-celled, two valved, with the valves gaping outwardly at the sides; seeds imbricate. There are three species.

MACROLOBIUM, in botany, a genus of the Triandria Monogynia class and order. Natural order of Lomentaceæ. Leguminosa, Jussieu. Essential character: calyx double, outer two-leaved, inner one-leaved; petals five, upper one very large, the rest small, equal; germ pedicelled, legume. There are three species, all of them tall trees, from sixty to eighty feet in height; they are natives of the large forests of Guiana.

MACROPUS, the kanguroo, in natural history, a genus of mammalia of the order Feræ. Generic character: six front teeth in the upper jaw, emarginated; two in the lower, and very long, sharp, large, and pointing forwards; five grinders on each side of the upper and under jaw, distant from the other teeth; fore legs very short; hind ones very long; the female with an abdominal pouch. This is one of the most curious of all the animals discovered on the continent of New South Wales, where it was observed by some of the sailors of Captain Cook in the year 1770. When full grown, it weighs about 150 pounds. Its head somewhat resembles that of a deer, but is destitute of horns; its countenance is gentle and complacent; its colour is of a pale brown; its length from the nose to the tail is between four and five feet, and the length of the tail is about three feet. Its general position, when resting, is that of standing on its hind feet, on their whole extent to the knees, and its fore feet are frequently employed, like those of the squirrel, as hands. They are often, however, laid on the ground, and the kanguroo is often seen in this posture, feeding. Vegetables, and particularly grass, constitute its only nourishment. In its rapid motions, however, the fore