The phenomena arising from the force of cohesion are innumerable. The spherical form of rain-drops; the difficulty of detaching a plate of glass from the surface of water; the force with which two plane surfaces adhere when pressed together; the drops that cling to the window-glass in a shower of rain—are all effects of cohesion entirely independent of atmospheric pressure, and are included in the same analytical formula (N. 162) which expresses all the circumstances accurately, although the laws according to which the forces of cohesion and repulsion vary are unknown. It is more than probable that the spherical form of the sun and planets is due to the force of cohesion, as they have every appearance of having been at one period in a state of fusion. A very remarkable instance has occasionally been observed in plate-glass manufactories. After the large plates of glass of which mirrors are to be made have received their last polish, they are carefully wiped and laid on their edges with their surfaces resting on one another. In the course of time the cohesion has sometimes been so powerful, that they could not be separated without breaking. Instances have occurred where two or three have been so perfectly united, that they have been cut and their edges polished as if they had been fused together; and so great was the force required to make the surfaces slide that one tore off a portion of the surface of the other. In liquids and gases the forms of the particles have no influence, they are so far apart; but the structure of solids varies according to the sides which the particles present to one another during their aggregation. Nothing is known of their form further than the dissimilarity of their different sides in certain cases, which appears from their reciprocal attractions during crystallisation being more or less powerful according to the sides they present to one another. Crystallisation is an effect of molecular attraction regulated by certain laws, according to which atoms of the same kind of matter unite in regular forms—a fact easily proved by dissolving a piece of alum in pure water. The mutual attraction of the particles is destroyed by the water; but, if it be evaporated, they unite, and form in uniting eight-sided figures called octahedrons (N. 163). These however are not all the same. Some have their angles cut off, others their edges, and some both, while the remainder take the regular form. It is quite clear that the same circumstances which cause the aggregation of a few particles would, if continued, cause the addition of more; and the process would go on as long as any particles remain free round the primitive nucleus, which would increase in size, but would remain unchanged in form, the figure of the particles being such as to maintain the regularity and smoothness of the surfaces of the solid and their mutual inclinations. A broken crystal will by degrees resume its regular