CHAPTER IX.

110. What does pneumatics teach? How can you show that air is material? How that it has weight? What is its weight compared with that of water?

111. What is said of the air's being attracted by the earth? Explain why some things rise and others fall in air. How thick is the earth's air-covering?

112. How is the height of the atmosphere ascertained? At what rate does the earth move round the sun? How does it carry along the air with it? State the influence which gravitation has upon the density of the air at different heights.

113. Give the comparison of air to wool. What is said of hydrogen and balloons? In what are gases and liquids alike, and what are the results of the similarity? What is the amount of pressure of the atmosphere on each square inch of surface? Give the calculations in regard to this pressure.

114. Show why the great pressure of the air does not produce destructive effects. Describe the air-pump.

115. Explain by Fig. 95 the plan and working of the air-pump.

116. State some of the experiments with the air-pump. How can you prove that air, like water, presses equally in all directions? State the comparison about the fish.

117. What is said of the Magdeburg hemispheres? Give the experiment with mercury. Explain the operation of the boy's sucker.

118. Give the statements about sucker-like arrangements in animals. State the experiment of the bladder and weight. Give the experiment with the India-rubber bag.

119. State the experiment with the egg. Explain the operation of the hydrostatic balloon.

120. Explain the operation of the Cartesian image. What is said of the presence of air in various substances?

121. What is said of the elasticity of air? Describe and explain the condenser.

122. Describe and explain the gasometer. Show how the air-gun operates. Explain the pop-gun.

123. Explain the operation of gunpowder. Explain that of steam. What is said of retardation by condensed air in gunnery?

124. Describe and explain what is represented in Fig. 113. Explain the collection of gases in the pneumatic trough.

125. Explain the experiment represented in Fig. 115. What is said of tapping a barrel? What causes the gurgling sound when a liquid is poured from a bottle? How high a column of water will the pressure of the atmosphere sustain? How do you find from this the pressure of the air on every square inch of surface? How high a column of mercury will the atmosphere sustain?

126. Explain the barometer. Relate the incident given by Dr. Arnot.

127. Why would not a water-barometer answer? What is said of the barometer as a measurer of heights? How is the boiling point influenced by the amount of the air's pressure? Give the experiment with ether.

128. State the experiment with the flask. What would happen to liquids if the atmosphere were removed from the earth? Explain the operation of the syphon by Fig. 117.

129. Explain what is represented by Fig. 118.

130. Explain the uses of the syphon. Explain the operation of the Cup of Tantalus.

131. How are intermitting springs accounted for? Explain the operation of the common pump.

132. Why does the water rise in the pump? How is sucking done? Explain the forcing pump.

133. Explain the fire-engine.