CHAPTER X.

134. What is said of the universality of motion? What of attraction as a cause of motion? What of heat? What of chemical agencies? What of life?

135. What is meant by saying that action and reaction are equal? State the illustrations of this truth which are given. Describe Barker's mill.

136. Give the comparisons to the operation of a spring, of firing of a cannon, and the throwing of stones from the crater of a volcano. What is said of the jumping of a man from the ground?

137. What is said of the reaction in the case of a hopping bird? Illustrate the inertia of matter as shown in the communication of motion. Give the illustrations of the fact that time is required to communicate motion to bodies.

138. Give illustrations of inertia as shown in the disposition of motion to continue.

139. Describe and explain the equestrian feat represented in Fig. 127. What is said of skill in jumping from a moving carriage? Relate the case in court which is stated.

140. What is said of the course of bodies thrown into the air? What of a man falling from a mast-head?

141. What is said of the atmosphere as revolving with the earth? What rapid motions are we subjected to when we speak of ourselves as at rest? Why are we insensible to these motions?

142. Follow out in full the comparison of the steamboat. What is the difference between absolute and relative motion? What is said of absolute rest?

143. Illustrate the truth that all the motions which are apparent to the eye are slight differences in the common absolute motions. What are the obstacles to motion? How is the motion of a stone thrown upward destroyed? What causes and what opposes its descent?

144. State and explain the experiment with the lead and feather. Explain the operation of the water-hammer. Show the relation of bulk to the resistance of liquids and gases.

145. Illustrate the relation of bulk to the motion of solids, produced by moving gases and liquids.

146. What is said of the opposition of gravitation to water and air in moving solids? What difference does the presence of obstacles make in the relation of force to velocity?

147. State the law of the relation of force to velocity, and illustrate by Fig. 136. What are some of the practical applications of this law? What is said of the relation of shape to velocity? What is said of the shape of fishes?

148. What is said of the shapes of boats? What of the management of the webbed feet of water-fowls? What of the wings of birds? What is said of friction as an obstacle to motion? What of it as a cause to motion? Illustrate fully in the case of the wheel.

149. What is said of the friction of liquids in tubes? What is the effect of sudden turns in pipes? What is the arrangement of arteries in the heads of grazing animals? Illustrate the difference of friction in small and large pipes by Fig. 131.

150. What is said of the effect of friction in brooks and rivers? In what part of a stream does the water move most rapidly? Explain the formation and breaking of the crest of waves rolling over a beach. What is said of the velocity of rivers as affected by friction? Explain the formation of waves.

151. What is it that really advances in the forward movement of a wave? Give the comparison mentioned. What is said of the height of waves?

152. What is momentum? Upon what two things does it depend? Illustrate this dependence. Explain Fig. 133.

153. Give the illustration of the musket-ball and cannon-ball. Give that of the plank. That of the candle. That of the air.

154. What is said of the expression, quantity of motion? Under what circumstances may a single impulse produce a great velocity? What examples have we of this? How is it with the motions that we see around us? What is said of the fall of bodies to the earth?

155. Give examples from muscular action. Give that of the arrow. Give that of gunpowder. What is said of the arrest of great velocities? Give the illustrations in regard to cannon-balls.

156. State and explain the feat of the anvil. Give examples from common efforts and labors.

157. Explain the communication of motion in the case of elastic bodies by Figs. 133 and 134. What is said of the reflection of motion?

158. What is said of the uniformity of motion? What of its uniformity in velocity? State by what means we calculate as to time.

159. What is said of the sun-dial? What of the hour-glass? What of Galileo and the pendulums? Explain the operation of the pendulum.

160. Explain Fig. 137. Explain the operation of the gridiron pendulum by Fig. 138.

161. What is said of the disposition of motion to be straight? Why is motion never straight, so far as we know? How can we make motion very nearly straight? Give the illustration of the bullet in full.

162. Give the illustration represented in Fig. 141. What is compound motion? Illustrate straight compound motion.

163. Explain Fig. 143.

164. Explain what is represented Figs. 144, 145, and 146.

165. Explain Fig. 147. How is curved motion produced? Give the illustration of the ball and string. What are centrifugal and centripetal forces?

166. What are these two forces in the revolution of the earth around the sun? Give various illustrations of the operation of centrifugal force.

167. What is said of the formation of bends in rivers?

168. Show how eddies and whirlpools are formed. How is the centrifugal force used in the art of pottery. How in making window-glass?

169. Describe and explain the operation of the steam-governor.

170. What is said of the agency of the centrifugal force in shaping the earth?

171. Explain the operation of the apparatus represented in Fig. 154. What are the forces which act on a projectile? What is said of balls thrown horizontally from cannon with different velocities?

172. Show by Fig. 155 why a ball dropped from the mouth of a cannon will fall to the ground in the same time that one fired from it will. By What two forces is a falling body acted upon?

173. Explain Fig. 156. What is the course of a ball dropped from a railway car or from a mast-head? Give the comparison between the cannon-ball and the moon.

174. What is said of the velocities of the heavenly bodies?