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. 89. Whence comes the name Artesian? What is stated of a well in Paris? What of the situation of London? Why is the pressure of a liquid in proportion to its depth? Give the illustrations of this mentioned in § 122. 90. Explain Fig. 75. 91. What is said about the construction of dams and brewers' vats? Explain the lateral pressure of liquids. Show the difference between a liquid and a solid in this respect. 92. Show how the earth's attraction causes the lateral pressure by Figs. 77 and 78. Give the view presented in § 124. 93. What is said of the proposed ship canal between the Mediterranean and the Red Sea? Show that pressure in liquids is equal in all directions. 94. Give the illustrations in § 126. Show that the upward pressure in a liquid is as the depth, and that this is produced by gravitation. 95. State the experiment represented in Fig. 82. Give the experiment with the tube and India-rubber. 96. State the examples given of great effects produced by small quantities of a fluid. Explain these effects by Fig. 83. 97. Explain Fig. 84. 98. What is the Hydrostatic Paradox, and why is it so called? Describe and explain the Hydrostatic Bellows. 99. Describe and explain Bramah's Hydrostatic Press. CHAPTER VIII. 100. Define specific gravity. 101. What is the most obvious way of ascertaining the specific gravities of different liquids? Explain the sinking of heavy substances in water. Explain the rising of light substances in water. Explain what is illustrated in Fig. 87. 102. Explain Fig. 88. Explain Fig. 89. 103. Give the illustrations in § 138: lifting a stone; raising a bucket; and raising the arm in a bath. Relate the anecdote of Archimedes. What is said of boats and life-boats? What of estimating the weight of the load in a canal-boat? 104. What is said of the specific gravity of birds? Of insects? Of fishes? What of the specific gravity of the human body, and of the prevention of drowning? 105. Give the reasons why so many are drowned that might easily be saved?