CHAPTER XI.

174. What are the Mechanical Powers? Why is the term power not strictly proper?

175. Explain the terms power, weight, and fulcrum. What is said of the use of the lever? What is the lever of the first kind? What is said of its force?

176. What is said of scales? What of steelyards?

177. Give examples of the first kind of lever. Show by Fig. 159 that there is no gain of power in this lever.

178. Give the illustration of the see-saw. What is said of Archimedes's lever?

179. State the analogy between this lever and the Hydrostatic Bellows, Bramah's Press, etc. What is the lever of the second kind? Apply the rule of equilibrium to it. Show how the common wheel-barrow is a lever of this kind.

180. Give other examples of the second kind of lever. What is lever of the third kind? How does this differ from the other two kinds? Apply the rule of equilibrium to it.

181. Give examples of the third kind of lever. Show how it acts at a mechanical disadvantage in the different examples mentioned. State in full what is said of muscular action.

182. Explain by the figures the operation of compound levers.

183. State the comparison between the lever and the wheel and axle. What is said of the common windlass?

184. Describe and explain the capstan. What are its chief uses? What is said of the fusee of a watch?

185. Describe the arrangement of the fixed pulley. What are its uses?

186. Describe the arrangement of the movable pulley. Show how the relation of the power to the weight is estimated in the case of compound pulleys.

187. Explain the mechanical advantage of the inclined plane. Give examples of it.

188. What is said of roads? Give the comparison of the wedge to the inclined plane. How is the power of the wedge estimated? Give examples of the wedge.

189. What is said of the screw? Show by Fig. 180 how the force of the screw is estimated. What are some of the uses of the screw?

190. Give the estimate of the power of the screw and lever as used together. How can you show that there are really but three mechanical powers? What is said of these as composing tools and machinery? What is said of friction in machinery?

191. What is the first advantage of the mechanical powers which is mentioned? Give the illustrations. What is the second advantage? Give the illustrations.

192. What is the third advantage? Give examples. How is the velocity of motion in machinery usually varied? What is the fourth advantage? Mention examples. Describe the instrument called a Lewis.

193. What is said of the title by which Aristotle distinguished man from other animals?