plate, the mercury will instantly recover its globular figure, and push up the glass before it.

In both these experiments we see that there exists an attraction between the particles of mercury; in the first, the globules which are in contact with the plate of glass leave this substance completely, they attract each other, and form a sphere greater in bulk. A mere inert fluid would in any case retain the figure it once possessed. It could not be endued with a globular form unless a real reciprocal attraction among its particles took place, which in the latter experiment is still more strking, for it there is not only superior to gravitation, but actually over. comes an external force.

EXPERIMENT III.

If a glass tube of a fine bore be immersed in water, contained in any vessel, the fluid will ascend to a certain height within the tube above its level, and its elevation in several tubes of different sizes will be reciprocally as the diameter of their bores.

This kind of attraction, which takes place as well in vacuo as in the open air, has been called capillary attraction. It is this attraction which causes water to rise in sponge, cloth, sugar, sand, &c. for all these substances may be considered as fine tubes in which the fluid ascends.

REMARK...The ascension of fluids in glass tubes of a fine bore succeeds best when the inside of the tube has been previously moistened, which may conveniently be done by blowing through it with the mouth. And if the water be coloured with a little red or black ink its ascension will be more obvious, particularly if the tube be held against a sheet of white paper.

EXPERIMENT IV.

If two plates of glass, previously wetted, be made to meet on one side, and be kept open at the other, at a small distance, by the interposition of a shilling, or any other thin substance, and then immersed in water, the fluid will ascend between the two plates unequally. Its upper surface will form a curve, in which the heights of the several points above the surface of the fluid will be to one another reciprocally, as their perpendicular distance from the line

in which the plates meet. The ratio of this attraction is, therefore, as the squares of the increments with which the plates open.

Here, then, we have two other instances that an attraction prevails among the particles of bodies. For in both cases part of the fluid has left the contiguous mass, contrary to the laws of gravitation. It is drawn up, as it were, or attracted, by the tube or plate of glass.

EXPERIMENT V.

If we immerse a piece of tin, lead, bismuth, silver, or gold, in mercury, and draw it out again immediately, the mercury will attract the metal, and the latter will carry with it a portion of the former, which will stick to it so obstinately as to be inseparable by mere friction.

There exists, therefore, an attraction between the different metals brought in contact with each other.

EXPERIMENT VI.

If we let fall into water a lump of sugar or salt, the particles of the water attract those of the sugar with a greater force than the last particles attract each other; they are therefore gradually carried off by the water, that is to say, the sugar is gradually dissolved.

The particles of the solid thus dissolved, are each of them surrounded and combined with a certain number of the particles of the fluid; hence they must be arranged in the liquid in regular order, and at regular distances from each.

EXPERIMENT VII.

If a small stick be dipped in water, or any other fluid, and drawn out again, a drop will be found hanging at the end of it in a spherical form. The drop is spherical, because each particle of the fluid exerts an equal force in every direction, drawing other particles towards it on every side as far as its power extends.

Thus the very formation of drops obviously demonstrates that there must exist a cause which produces that effect. This cannot be gravity, for, agreeable to experience, that is rather an obstacle to the formation of drops; since, by the weight of the particles, large globules rest8

VOL. I.

ing on solid bodies are flattened, and their regular spherical form prevented.

To explain this phenomenon there remains only the power of attraction, acting between the particles of the liquid body; for if it is supposed that the particles of a substance reciprocally attract each other with equal force, and their aptitude for being moved upon one another be great enough to overcome any impediment to their motion, it follows, by the principles of mechanics, that the equilibrium of the attractive forces can only take place when the mass has received a globular form.

Hence it is that all liquid bodies assume a spherical figure when suffered to fall through the air, or form drops. Whether the attractions of gravitation, or magnetism, of electricity, and of cohesion, be or be not considered as .. essentially the same, is not our business to consider here circumstantially; there is difference enough between them to allow a very accurate examination of each. We merely consider attraction as an unknown power, by which all bodies are urged towards each other as an agent, which acts constantly and uniformly in all times and places, and which is always diminishing the distances between bodies.. It is obvious that the distances of bodies are of two kinds, either sensible or insensible; consequently the changes produced by attraction must be either sensible or insensible. Hence the attraction of bodies naturally divides itself into two classes; those which act at sensible distances, and those which act at insensible distances. The attractions belonging to the first class must be as numerous as there are bodies situated at sensible distances; but it has been ascertained that they may be all reduced to three different heads, viz, gravitation, electricity, and magnetism. The first belongs to all matter, and therefore is universal: the other two are only partial, or confined to certain sets of bodies. The first extends to the greatest distances to which bodies are placed from each other: how far electricity extends, has not been ascertained. Magnetism extends, at least, as far as the semi-diameter of the earth. All bodies possess gravity; and it is supposed that the two other attractions are confined to certain subtile fluids which constitute a part of all those bodies which exhibit the attractions of electricity and magnetism. This may be so, but it has not and scarcely can be demonstrated.

SECT. II.

DIVISION OF ATTRACTION.

THOUGH we are unable to discover the cause of the mutual attraction, experience has proved to us that this agency follows certain conditions or laws; for similar phenomena always present themselves whenever the circumstances of experiment are the same.

Observation has taught us that the particles of bodies are of two kinds, either homogeneous or heterogeneous. By homogeneous particles, chemists understand particles composed of the same body; thus all particles of sulphur, &c. are homogeneous particles. By heterogeneous particles, chemists mean particles which compose different bodies; thus a particle of sulphur and a particle of mereury are heterogeneous particles.

In the early periods, when chemists perceived that the force here considered opposed their operations, being habituated to explain the effects they observed by certain. relations, or analogies, which they supposed to exist between bodies, they gave different appellations, to express this agency. The first agency is still called by physical writers corpuscular attraction, or attraction of aggregation; molecular attraction: attraction of cohesion, or the cohesive power.

The latter is termed chemical attraction, elective attraction, chemical affinity, or affinity of composition. But before we consider this subject any further, we shall give an idea of what has been called repulsion.

REPULSION.

PART VII.

IT was mentioned before (page 54) that all matter possesses, besides attraction, another power which is in constant opposition to the former. This agency, which is equally powerful and equally obvious, acts an important part in the phenomena of nature, and is called the power of repulsion. It is not less interesting to the chemical philosopher, than the powers of attraction.

AXIOM OF REPULSION.

All bodies are endowed with a certain power, whose constant tendency is to oppose their approach towards each other, or to remove the particles of matter to a greater distance.

SECT. I.

PROOFS OF THE ENERGY OF REPULSION.

THAT there exists a force which opposes the approach of bodies towards each other is evident from numberless facts.

Newton has shown that when a convex lens is put upon a flat glass, it remains at a distance of the 737 part of an inch, and a very considerable pressure is required to dimi