3. Thrust vertically two plates of glass into water, and gradually bring the surfaces near to each other. Soon the water rises between the plates, and rises higher as the plates are brought nearer. If their surfaces be mutually parallel and vertical, the water rises to the same height at all points between the plates, as shown at A (Fig. 9.) [Illustration: Fig. 9.] 4. If the plates be united by a hinge, and form an angle, the height to which the water ascends increases as the _distance_ between the plates decreases up to their line of junction, where it attains a maximum, as shown at B (Fig. 9.) 5. Decrease the _angle_ between the plates, and the water ascends higher, as shown at C (Fig. 9.) Thus it is seen that _the ascension varies inversely with the angle between the plates_; i. e., the smaller the angle, the higher the water ascends. 6. When a drop of oil is placed between two glass plates arranged as shown at A (Fig. 10), if the surfaces are not too far distant, and if the oil touches both surfaces, it will be seen to work its way to the junction of the plates; showing that _oil between surfaces has a tendency to flow towards the apex of the angle_. [Illustration: Fig. 10.] 7. Place a drop of oil on a taper piece of metal, as shown at B (Fig. 10). The oil will gradually recede from the point to a place where there is more metal, showing that _oil on surfaces has a tendency to flow towards the largest part_. [Illustration: Fig. 11.] 8. When a drop of oil is placed between two watch glasses arranged with flat and convex sides adjacent, as at A (Fig. 11), or with convex sides adjacent, as at B (Fig. 11), if the glasses are rigidly fixed in their relative positions the drop of oil can be shaken from its location only with great difficulty; the oil at C holding its place with greater tenacity than the oil at D. The foregoing phenomena are called _capillary action_, or _capillarity_. Capillary action is due to the forces of cohesion (20), and to the forces of adhesion (21.) ~23. Centrifugal Force.~--_The tendency of a body rotating round a point to escape from that point is called centrifugal force._ Place a small quantity of oil on the arm of a balance, near the arbor. Rotate the wheel rapidly. The oil is seen to flow towards the rim of the wheel. ~24. Absorption of Gases by Liquids~ depends on molecular attraction and motion. Water at a temperature of 0° cen. (32° f.), is capable of condensing in its _pores_ (17) six hundred times its own bulk of ammonia gas. The absorption of oxygen from the air causes some oils to become more viscous, to eventually become solid, without losing in weight, in fact sometimes gaining. Other oils dry up, or _evaporate_, leaving little or no residue. ~25. Force.~--_Force is that which can produce, change or destroy motion._