80. What is said of the phenomena treated of in Hydrostatics? What are the two characteristics of liquids? What makes a liquid have a level surface? Give the explanation. Give the comparison of the shot.
81. What is said of water as a mirror? Show that the surface of a liquid is not strictly level. If the earth had no elevations of land why would it have a perfectly globular covering of water?
82. What is a so-called perfectly level surface? What is the variation per mile from a real level? Describe the spirit-level. Give the comparison between a trough and a river.
83. What is said of the declivity of rivers? How have some rivers been made? What is stated in regard to the River Danube?
84. What is stated about the Lake of Geneva? Describe the arrangement of canal locks.
85. How are canals used for working machinery? Give various illustrations of the tendency of water to be on a level.
86. Describe the arrangement represented in Fig. 71, and give the explanation.
87. Describe a foolish man's plan for perpetual motion, and give the reason of its failure. What is said of ancient and modern aqueducts?
88. Explain the operation of springs and Artesian wells.