thread, 300 yards long, has weighed only 24 grains. In odoriferous bodies, we have a still more striking illustration of very minute particles of a body being separated from one another. Perhaps you may not be aware, that the sensation of smell is, in every case, produced by particles called effluvia, which fly off from the odoriferous body, and come in contact with the nostril of the individual who smells it. This, however, undoubtedly is the case, so that you can just as little smell a rose, if none of its effluvia touch your nostril, as you can taste an apple without applying any part of it to your tongue. Now these effluvia are not only so small, as to be quite invisible, but their excessive minuteness will still better be estimated, when you consider how soon every part of a room is perfumed by a nosegay or a smelling-bottle, and the vast number of effluvia necessary for this purpose, while as yet there has not been the slightest sensible diminution, either in the bulk, or the weight, of the original body. Every particle of matter, notwithstanding its separation from the body, to which it originally belonged, however minute in itself, or invisible to human eyes, retains in its separate state all the essential properties of body. It may be changed, indeed, in point of form and qualities, as well as of dimension; may be converted from a solid into a liquid, or from a liquid may vanish into thin air; but not one created atom (so far as we have reason to believe) ever perishes or is annihilated. Not one of them is lost, but all continue, in one state or another, to fulfil the ends for which they were destined, by their all-wise Creator, in the system of his universe. When a body has been burnt to ashes, that part of it, which continues visible, is sadly shrunk indeed in dimensions, but the part which escaped in vapour, though no longer visible to the eye, has not perished, but exists as truly, and in all probability as beneficially, as when united to the body, from which it has at length been disengaged.-V. INERTIA is that property of bodies, by which they resist any change in their present state. When a body is at rest, it will require force to put it in motion. When it is in motion, it will no less require force either to stop, to retard, or accelerate that motion. A stone thrown by the hand

would continue to move for ever through space, with unabated velocity, were it not for the resistance of the air, and the force of gravity (to be explained in a future article) by which it is brought to the ground.-VI. Another property of bodies, and one of the most important, is ATTRACTION, by which is meant that tendency, which subsists both between different bodies, and between the particles of the same body, to come together and unite. Were this property to cease, you would no longer see bodies falling to the earth; the earth itself would cease to perform its revolutions; nay its own fabric would instantly dissolve. It is of two kinds, Cohesion and Gravity on, which shall form the subjects of the two following articles.

ON COHESIVE ATTRACTION.

COHESION is that species of attraction, which operates among the small particles of bodies, when brought extremely close to each other. Were it not for the influence of this attraction among the particles of the same body, they would fall off from each other, and the most solid mass would crumble into atoms. It is this property, for example, which keeps all the particles of that slate in union. Were you to break it, you could not reunite its parts, because it would not be in your power to bring the particles again so closely together, as to admit of the operation of this species of attraction. It operates among liquid as well as solid particles. What else is it, which gives to every drop of water its spherical form? Why else is it, that, when two drops touch each other, however slightly, in any one point, they immediately run together, and unite in one larger globule? But, because a liquid is so constituted, that its particles are farther apart from each other than those of a solid, the cohesive attraction is, in the case of liquids, proportionally weaker. If you open the side of a vessel which contains a liquid, the particles of the liquid immediately separate and fall to the ground, which is not the case with respect to a solid body. The particles of air are still more distant from

each other, than those of liquid bodies, and hence, though there can be no doubt that they possess the same power of attraction, which belongs to the particles of other bodies, the operation of this power is lost. It thus appears that the operation of cohesive attraction is not equally strong in all bodies; and hence it is, that one solid is harder than another, one fluid is thinner than another. Those bodies in which this attraction operates most powerfully, are termed dense bodies: those in which it is weak are said to be rare. Thus gold is a denser solid than wood; water is a rarer fluid than quicksilver. It is a well-known puzzle among children, to ask whether a pound of lead or a pound of feathers is heavier? Every one, acquainted with the real meaning of the question, will at once answer, that the weight in both cases is precisely the same: but the dimensions of the pound of feathers are greater, than those of the pound of lead, because lead is a much denser or more compact body than feathers. It is by the weight, accordingly, that we are to judge of the density of a body. A dense body will of course be much heavier, than a rare one of the same dimensions, on account of the greater quantity of matter, which it contains.-There is a curious species of cohesive attraction, which remains to be noticed, known by the name of the capillary attraction (that is to say, the attraction of hairs), because the instruments of this attraction are slender tubes like hairs. If one of these tubes be immersed in water, the fluid will immediately rise to a certain height in the tube, in consequence of the particles of the fluid being attracted by the particles of the tube. If several tubes of different bores, but all extremely narrow, be employed, the liquid will rise to different heights in each. In those of which the bore is narrower, the liquid will ascend higher. Porous bodies, such as sponge, bread, linen, &c. are composed of natural capillary tubes, which afford illustrations of this species of attraction. If you dip the corner of a bit of sugar into water, the water immediately rises through the capillary tubes of the sugar, till it reaches its remotest particle. It is upon a similar principle that blot-paper operates when used for drawing up superfluous ink.-Hitherto we have only

been considering the operation of attraction in small and near particles, its operation in larger masses, though more remote, is left for the subject of a separate article.

ON GRAVITATION.

In the last article we considered that species of Attraction called Cohesion, which operates among the small particles of bodies when brought into close proximity to each other; we are now to consider that species of it called GRAVITATION, which operates also among large masses though placed at a remoter distance, with a force proportioned to the quantity of matter contained in these bodies. Every stone, which falls to the ground, is an example of this attraction: for what else is it, which occasions its fall, but the attraction of the earth? If there were no external force impelling or attracting it, why should it not, according to the general law of nature, explained in a former article under the name of Inertia, remain at rest? or can any reason be assigned, why it should not as readily fly up to the sky, or diverge to the right hand or to the left?

Were

there no other body in universal nature except the stone, there can be little doubt that it would remain quite stationary: neither would it possess any weight, for a single moment's reflection must satisfy you that this is not an inherent property of the stone, independ ent of its connexion with another body, but arises entirely from its tendency to fall to the earth. All this, however, which is now so satisfactory to every welleducated and reflecting mind, and which, when pushed to its necessary consequences, so clearly explains many of the grandest phenomena of nature, was utterly unknown till the year 1665, when the mighty discovery immortalized the name of Sir Isaac Newton, a philosopher of our own country. This discovery, glorious as it is, owed its origin to an incident of daily occurrence, and apparently of the most trivial nature. Sitting in his orchard one day, Sir Isaac saw an apple fall from a This single circumstance, so familiar to us all, called up, in his reflecting mind, a long train of thought,

tree.

with regard to the cause of the occurrence. He could account for it on no other principle, than the supposition of an attractive power in the earth. Carrying his reflections further, he was satisfied that this attraction is not peculiar to the earth, but subsists among all bodies whatever; that, as the earth attracts the bodies which come within the range of its influence, so itself and various other planets are, in like manner, attracted by the sun and thus, at length, did this great man disclose to an astonished world those laws, by which the wisdom of the Almighty Ruler had governed his universe, from the first hour of its creation, but which, during so many ages of its existence, "lay hid in night."In many cases the attraction of Cohesion predominates over that of Gravitation. Hence it is that the particles of a solid body continue united, in place of falling off to the ground, as is the case when the side is opened of a vessel containing a liquid. Thus how often do we see a projecting rock continue riveted to the cliff, in opposition to the strong force of gravitation, struggling to plunge it into the gulf beneath. The phenomena of capillary attraction afford an admirable illustration of the counteracting powers of cohesion and gravitation. We have seen, that, in the extremely slender tubes, by which this attraction operates, the liquid rises in opposition to the power of gravitation. But it rises only to a certain height, beyond which the gravity of the liquid will not permit it to ascend; namely, the point at which the gravitation and cohesion balance each other. From what has now been said, it will be easy to understand the reason, why the water rises to a less height in a capillary tube of a larger bore, and why, when the bore is still further extended, it ceases to rise at all.-We formerly stated, that Newton was led to the conclusion, that all masses of matter attract each other. Why then, it may be asked, do houses not move towards each other, or take their departure to a neighbouring mountain? The solution of this question is extremely easy. It has already been mentioned, that gravitation acts with a force proportioned to the quantity of matter. Now no body on the earth's surface contains nearly as much matter as the earth itself. Therefore the earth's own attraction pre