_Mrs. B._ That depends upon the situation of the materials; if those which are most dense, occupy the lower part, the stability will be increased, as the centre of gravity will be near the base. But there is another circumstance which more materially affects the firmness of their position, and that is their form. Bodies that have a narrow base are easily upset, for if they are a little inclined, their centre of gravity is no longer supported, as you may perceive in fig. 6. _Caroline._ I have often observed with what difficulty a person carries a single pail of water; it is owing, I suppose, to the centre of gravity being thrown on one side; and the opposite arm is stretched out to endeavour to bring it back to its original situation; but a pail hanging to each arm is carried with less difficulty, because they balance each other, and the centre of gravity remains supported by the feet. _Mrs. B._ Very well; I have but one more remark to make on the centre of gravity, which is, that when two bodies are fastened together by an inflexible rod, they are to be considered as forming but one body; if the two bodies be of equal weight, the centre of gravity will be in the middle of the line which unites them, (fig. 7.) but if one be heavier than the other, the centre of gravity will be proportionally nearer the heavy body than the light one. (fig. 8.) If you were to carry a rod or pole with an equal weight fastened at each end of it, you would hold it in the middle of the rod, in order that the weights should balance each other; whilst if the weights were unequal, you would hold it nearest the greater weight, to make them balance each other. _Emily._ And in both cases we should support the centre of gravity; and if one weight be very considerably larger than the other, the centre of gravity will be thrown out of the rod into the heaviest weight. (fig. 9.) _Mrs. B._ Undoubtedly. Questions 1. (Pg. 46) If a body be struck by two equal forces in opposite directions, what will be the result? 2. (Pg. 46) What is fig. 5. plate 2. intended to represent? 3. (Pg. 47) How would the ball move, and how would you represent the direction of its motion? 4. (Pg. 47) What is supposed respecting the forces represented in fig. 6? 5. (Pg. 47) How would the body move if so impelled? 6. (Pg. 47) If the forces are unequal and not at right angles, how would the body move, as illustrated by fig. 7? 7. (Pg. 47) How must a body be acted on, to produce motion in a curve, and what example is given? 8. (Pg. 48) When is a body said to revolve in a plane, and what is meant by the centre of motion? 9. (Pg. 48) What is intended by the axis of motion, and what are examples? 10. (Pg. 48) What is the middle point of a body called? 11. (Pg. 48) What is said of the axis of motion, whilst the body is revolving? 12. (Pg. 48) When a body revolves on an axis, do all its parts move with equal velocity? 13. (Pg. 49) How is this explained by fig. 1. plate 3?