We may now notice that species of attraction which does not extend to sensible distances. Such is found to obtain in the minute particles whereof bodies are composed, and which attract each other at or extremely near the point of contact, with a force much superior to that of gravity, but which at any distance from it decreases much faster than the power of gravity. This is termed the attraction of cohesion, as being that by which the atoms or insensible particles of bodies are united into sensible masses.

This latter kind of attraction owns Sir Isaac Newton for its discoverer, as the former does for its improver. But, besides the common laws of sensible masses, the minute parts they are composed of are found subject to some others, which are thus illustrated by Newton:-" In virtue of these powers," he says, "the small particles act on one another even at a distance; and many of the phenomena of nature are the result thereof. Sensible bodies act on one another in divers ways; and we thus perceive the tenour and course of nature. It appears highly probable that there may be other powers of the like kind; nature being very uniform and consistent with herself. Those just mentioned reach to sensible distances, and so have been observed by vulgar eyes; but there may be others which reach to such small distances as have hitherto escaped observation; and it is probable electricity may reach to such distances even without being excited by friction."

These phenomena, "in virtue whereof the particles of the bodies above mentioned tend towards each other," Newton calls by a general indefinite name attraction, which is equally applicable to all actions by which distant bodies tend towards one another, whether by impulse or by any other latent power; and from hence he accounts for an infinitude of phenomena, otherwise inexplicable, to which the principle of gravity is inadequate. "Thus,” adds our author, "will nature be found very conformable to herself and very simple, performing all the great motions of the heavenly bodies by the attraction of gravity, which pervades those bodies, and almost all the small ones of their parts, by some other attractive power diffused through the particles thereof. Without such principles, there never would have been any motion in the world; and without the continuance thereof motion would soon perish, there being otherwise a great decrease or diminution thereof, which is only supplied by these active principles."

The attraction which subsists between the particles of fluid bodies was first investigated by the Academy del Cimento. But the completest series of experiments on capillary action was made by our countryman Hauksbee. He proved that it is not affected by atmospheric pressure, and succeeds equally well in vacuo; he showed the ascent of water and other liquids between proximate glass plates, and compared it with the rise in narrow tubes; and he ascertained the elevation to be always inversely as the width of the bore or the separa. tion of the plates. He found that the same property belongs to marble and brass, and remarked the ascent of water in an open barometer tube filled with fine ashes. Dr. Brooke Taylor likewise performed several ingenious experiments on this subject having joined two plates of glass at their vertical sides so as to form a sharp wedge, he dipped it in a vessel of water, and observed the liquid to rise and form a rectangular hyperbola, thus clearly exhibiting the relation of the ascent to the interval between the proximate surfaces. But he pursued the phenomena of corpuscular attraction still further, and measured the adhesion of a disk of glass to water and mercury. Seventy years afterwards this enquiry was resumed by the celebrated Guyton Morveau, who endeavoured to ground upon it the chemical theory of elective attraction. The attempt however was fallacious, because the force required to detach a disk of glass, marble, or metal, from a surface of water or mercury, is not a single effort, but combines the adhesion of the liquid particles to the solid with their cohesion to each other. In 1718, Dr. Jurin, being led to examine the phenomena of capillary attraction, proposed a theory for their explication which seemed at least plausible. He

rightly ascribed the rise of water in the cavity of the tube to the close attraction of the internal surface of the glass, though he did not perceive the way in which that force must act. He fancied the suspension of the slender column of liquid to be caused by the attraction of the ring of glass immediately above its summit. But such an assumption was quite illusory; for the ring below that limit would evidently exert an equal force in the opposite direction, and thus extinguish the influence of the former.

It is, however, to Segner that we are indebted for the first accurate view of the theory of capillary attraction. He took up the subject in 1754, and gave a different solution, distinguished by its depth, ingenuity, and general accuracy. Assuming as a principle, that the attractive energy is confined to a mere exterior film of the liquid, he found the curve of the upper surface to be what is called the Lintearia, or the cavity of an inflated sail formed by a uniform tension. The results he obtained were perfectly accordant with the phenomena, except in the figure of a drop of water, in the determination of which he had, from overlooking the double curvature, committed a small error.

Nearly half a century more elapsed before any further attempt deserving notice was made to improve the theory of capillary attraction. In 1804, the late lamented Dr. Thomas Young resumed the investigation of this subject, and obtained a very complete solution, but which required the admission of a repulsive force among the particles of the liquid at a certain small distance. These investigations were subsequently resumed by Mr. Ivory, who threw considerable light on the subject of capillary attraction.

The attraction which results from a disturbance in the electrical equilibrium may next be adverted to. There were some very ridiculous doctrines taught by the ancient schoolmen in connection with this species of attractive energy. They believed that there were sympathies between different bodies which caused them to attract others and elicit light when they were excited by friction. The whole train, however, of these absurdities have been swept away by the discoveries of Franklin, Davy, and Faraday. . The apparatus employed by the early experimentalists in this branch of science, though very inefficient, was yet sufficiently simple. Mr. Grey, who was resident in the Charter House early in the last century, was an ingenious electrical philosopher. He is represented with his apparatus in the subjoined sketch. He was enabled to raise light pieces of paper by exciting a glass tube, and his apartments became the resort and wonderment

of the little knot of philosophers who flourished at the period, and whose proceedings were carefully chronicled by several members of the Royal Society.

This ingenious philosopher was also enabled to give a spark to the finger when presented to the tube, as is shown in the other portion of the figure. When Mr. Grey wished to increase the power of his apparatus, he went out into his balcony, and then, by the agency of a long piece of wire suspended by a silk thread, he obtained a sufficient conducting sur

face for his purpose. We cannot in the present place pause to compare this pigmy and illassorted apparatus with the giant machines employed in the Teylerian Museum, which melted bars of metal, burnt combustible bodies, illuminated the apartment, and indeed exhibited all the terrific phenomena of the very bolts of heaven. But it is a curious and interesting task to trace these incipient efforts of philosophy in her infancy, as a little more glass and metal, aided by a little more experience, would have converted Mr. Grey's apparatus into one fitted for the lecture-table in the present day,

Strictly speaking, the science of mechanics includes the laws of matter, motion, and force,

The first of these possesses the attributes of solidity and inertiæ; it is divisible as far as our senses or even our imagination can go, but we are certain that its ultimate particles must be indivisible, or at least that they are never divided in the operations of nature. In the proper sense of the term, no matter is solid; for no mass is destitute of pores into which other substances may not be introduced. Thus wood contains air between its fibres, and air contains water diffused in it in the state of vapour. With reference to the actual solidity of the particles of which firm bodies are composed, it appears certain that they act on each other without really being in contact, by means of powers connected with them, put in operation by the Author of all things. Where the forces act with great intensity, the body presents the quality of hardness, resisting any attempt to separate the particles: where their sphere of action is of some extent, it is termed elastic, and possesses the power of resuming its original dimensions, when the power which compressed or extended it ceases to act. If the repulsive force be diminished, or the cohesive increased, the bulk of the body must diminish, as when it is compressed by an external force, or when its temperature is reduced. That being always an antagonist to cohesion, by its action solids become fluid, and liquids are changed into vapours, the intermediate steps being marked and measured by their expansion.

Inertia is a term invented to express that quality of matter by which it is indifferent as to rest or motion, that passiveness to every impulse which is so decidedly its attribute. Were there no other being in the universe it must be for ever unmoved and dead; were it once put in motion it must move for ever: and they who dreamed that the universe was caused by a fortuitous concourse of atoms showed their absolute want of observation.

That matter has

no power to put itself in motion every one will readily admit; but it is thought by some difficult to conceive how it can be indifferent to rest. At the first view it appears that all motions decay, and that, as some cause is required for their beginning, so it is necessary to maintain them; but, if we examine more minutely, we find that there exist around us phenomena capable of producing this loss of motion, and to which therefore it must be attributed, such as the resistance of the air, friction, stiffness of cordage, &c. If these be diminished (for they can never be removed), the motion is prolonged, and to such a degree as decidedly shows that if they were entirely removed the motion would be perpetual. The quality of absolute inertia belongs only to matter in the abstract; for every atom of it with which we are acquainted acts on others, being the vehicle of the energies by which the Governor of the universe has ordered his works to be swayed.

We have seen that gravitation resides in every particle of the solar system; electricity, magnetism, and heat, are in this globe almost omnipresent; and the actions of bodies on light, and the play of chemical affinities, indicate the existence of countless forces resident in matter. But the effects of these are obviously distinct from the formation of matter itself, and cannot be explained by any material agency: besides, we see that they cannot affect our conclusions, for in our enquiries we are aware of their influence, and allow for it, considering them as unconnected with matter; as instances, we reason as if rocks were inflexible, cords pliable, and machinery void of weight, but merely conveyers of forces, and we obtain conclusions, true only in the abstract, but capable of being corrected for particular circumstances.

The sources of motion with which we are acquainted are, the energy of animated beings, the forces to which we have already alluded as implanted in matter, and the impulsion of a body which communicates its motion to another, this last being scarcely entitled to the name of force.

Where one body communicates force to another, the quantities of motion lost and gained are equal, and they are measured by the quantities of matter multiplied into the velocities; thus, if the striking body be doubled, its quantity of motion must be doubled, and if its velocity also be doubled its motion is fourfold; and in the same way when a disturbing force

generates motion its energy is as the product of the mass moved into the velocity produced. The strength of animals is more manageable than most other movers; but the employment of it is narrowed by the limited velocity which they can produce, and by the variable nature of their exertions; and it is too often attended with circumstances revolting to humanity.

The most powerful forces which man has subjected to his industry are those of gravitation and expansion. A mass of solid matter descending from a height, a stream of water, and a current of air, afford potent movers, which are made useful by means of machinery. Still more energetic are the forces causing expansion; and the elastic force of steam, and the yet more formidable agency of gunpowder, give the means of exciting almost unlimited velocity. To devise the means of applying these to use in the most advantageous manner is the object of practical mechanics, and for the perfection of this art both theory and experiment must lend their aid, as it is equally absurd to despise the investigations of the analyst without understanding them, and to found elaborate researches on false data.

Now the mechanical powers, as they are called, are usually employed to counteract the effects of gravitation, and to produce effects which the unassisted powers of man could not otherwise accomplish; and it is astonishing how small is the change which time has effected in their arrangement. It is true that amazing advantages have been effected by their combination, but the elementary instruments were as well understood by Archimedes as by the philosophers of the present day.

Without such instruments it would rarely be possible to use any force except human strength, and the employment even of this would be very limited. In the least complicated of all mechanical efforts, that of raising a large weight as soon as it exceeded the strength of one labourer, a great difficulty would be experienced; and the average force of each individual would be proportionably less as their number increased. If, however, one man, by the aid of any mechanical instrument, can act against a force equal to tenfold his ordinary strength, and at the same time it be easy to combine the efforts of many with undiminished effect, there can be no limits to the tasks which they may perform. No force is generated in machines. All that is effected by them is to move a light body with speed, or a great weight slowly; and therefore they who have sought for a perpetual motion by the aid of machinery have but displayed their ignorance of the first elements of mechanics.

The implements employed by the early mechanics were usually of the most simple character; a bar of wood, or a mound of earth, appears to have served for the elevation of large stones that even in the present day would seem to require much more complicated apparatus. In our own island, even after the invasion of the Roman power, when the arts and civilization of the conquerors of the world might have taught the aboriginal inhabitants the use of mechanical inventions, we still find them in the most lamentable state of ignorance. The vast horizontal stones which still form part of the Druidical circle at Stonehenge have evidently been raised by the agency of an inclined plane of earth; but, as this subject has excited much controversy amongst antiquaries, we had better illustrate the matter by a diagram.

If we suppose the perpendicular stones

to be erected, as shown in the figure, a mound of earth, forming an inclined plane, will readily suffice for placing the horizontal stone in its proper situation. The earthen plane may afterwards be removed, and thus

all trace of the original process destroyed. By an arrangement of this kind, the celebrated traveller Belzoni was enabled to remove masses of stone which would otherwise have defied his utmost exertions. It must still, however, be borne in mind that a much greater

loss of power from friction results from the use of these primeval machines than when the improved implements of science are resorted to. In ancient times, whole nations of slaves were employed to raise pyramids and erect monuments, by which their energies were wasted and their lives ultimately destroyed, merely to gratify the caprice of a successful invader; while at the present period we are enabled to effect much greater works by the agency of machinery, and that too almost unassisted by human labour. An ingenious foreigner has published an estimate of the mechanical force set in action by the steam-engines of this country. He supposes that the great pyramid of Egypt required for its erection the labour of more than 100,000 men for twenty years; but that if it were required again to raise the stones from the quarries, and place them at their present height, the action of the steamengines of England, which are managed at most by 36,000 men, would be sufficient to produce the same effect in eighteen hours.

A good notion of the ordinary pursuits of the early mechanicians may be derived from their singular predilection for the construction of automata. The labour of a life-time was frequently devoted to the construction of a single figure. Among the ancients, Dædalus was famed for constructing machines that imitated the motions of the human body. Certain statues of his, it is said, had the power of moving about, and would run away unless forcibly detained. Aristotle speaks of these in his treatise De Anima, and affirms that the effect was produced by concealed quicksilver. This, however, could not be the case, unless the automata moved on a descending plane, like the Chinese toy called a tumbling mandarin, which, by means of mercury contained in the cavity of its body, is made to descend a series of steps. Friar Bacon and Albertus Magnus both exercised their ingenuity in the construction of androides, which appeared so wonderful to the ignorant multitude as to draw upon their inventors the dangerous imputation of being addicted to magic. Bacon is said to have constructed a brazen image capable of speaking; and Albertus Magnus formed an artificial man, in the construction of which he spent thirty years of his life. This, we are told, was broken to pieces by Aquinas, who came to see it, purposely, that he might boast how in one minute he had rendered fruitless the labour of so many years.

But these singular mechanical contrivances have also engaged the attention of many modern mechanics. Vaucanson invented some which are thus described by Beckman :"One of them, which represented a flute-player sitting, performed twelve tunes, and, as we are assured, by wind issuing from its mouth into a German flute, the holes of which it opened and shut with its fingers. The second was a standing figure, which in like manner played on the provençal shepherd's pipe, which it held in its left hand, and with the right beat upon a drum. The third was a duck, of the natural size, which moved its wings, exhibited all the gestures of that animal, quacked like a duck, drank water, ate corn," &c.

A celebrated machine of this kind, constructed by the younger M. Droz, of the Chaux de Fronds, is thus described by Mr. T. Collinson, in a letter to Dr. Hutton, published in that gentleman's Mathematical Dictionary :- "Permit me to speak of another automaton of Droz's, which several years since he exhibited in England, and which, from my personal acquaintance, I had a commodious opportunity of examining. It was a figure of a man, I think the size of life. It held in its hand a metal style: a card of Dutch vellum being laid under it, a spring was touched, which released the internal clock-work from its stop, when the figure immediately began to draw. M. Droz, happening once to be sent for in a great hurry to wait upon some considerable personage at the west end of the town, left me in possession of the keys which opened the recesses to all his machinery. He opened the drawing-master himself, wound it up, explained its leading parts, and taught me how to make it obey my requirings, as it had obeyed his own: M. Droz then went away. After the first card was finished, the figure rested. I put a second, and so on to five separate