  [Teachers differ much in their plans of conducting recitations. Some are very minute in their questions; while others go to the other extreme, and merely name the topics, the pupils being expected to give in full what is said upon them. Neither of these plans should be adopted exclusively, but the mode of recitation should be much varied from time to time. This variety is somewhat aimed at in the questions which I have prepared, though in no case are the questions as minute as they should occasionally be made by the teacher. The numbers refer to the pages. It would be well to have the pupils draw many of the figures upon the blackboard, and then recite from them. By drawing the simplest figures first sufficient skill may be acquired to enable the pupil to draw those which are quite difficult.] CHAPTER I. 13. What is said of the distinction between matter and spirit? What of Bishop Berkeley's ideas? What of Hume's? 14. What is the origin of the word spirit? What is the relation of the senses to the spirit? What is said of the effects of matter on the senses? What are the forms of matter? 15. Illustrate the difference between elastic and non-elastic fluids. What is said of the union of the particles of a solid? Give the difference noted between different solids. How does a liquid differ from a solid? Give particularly what is said of water. 16. What is said of the particles of gaseous substances? What of the atmosphere? What of the vapor in it? What is said of the entering of liquids and gases into interstices? What of the mingling of gases with liquids? Give the illustration in regard to fishes. 17. What is said of the solution of solids in liquids? What of the evaporation of water in the air? Illustrate the influence of heat on the forms of matter. What is said of the thermometer? What of mercury, water, and iron in relation to the liquid state? What is said of our knowledge of matter? 18. What was the supposition of Newton about the composition of matter? What is said of the changes of matter? What are the imponderable agents, and why are they so called? CHAPTER II. 19. What is said of variety in the properties of matter? What of the divisibility of matter? 20. What is said of gold-leaf, and of the wire of gold-lace? What 21. What is said of the dust of the puff-ball? What of pollen? What of the dust rubbed from a moth's wing? What of guano? What of the glazing of visiting-cards? What of the minuteness of some animals? 22. What is said of the Deity in relation to minute animals? What is said of substances called porous? What of those in which there are no pores apparent? What proof is there that all substances have spaces in them? 23. What is said of the amount of space in gases and vapors? Give the statement in regard to steam. What is said of solutions of solids in fluids? What of evaporation? What of the diffusion of odors in the air? 24. What is the relation of heat to space in matter? Upon what do density and rarity depend? Explain tenacity. What is said of this property in gases and liquids? 25. How is the comparative tenacity of substances ascertained? Give the comparative tenacity of various substances. What animal substances have great tenacity? What is said of the value of tenacious substances? 26. What is said of hardness? What of flexibility and brittleness? 27. Give examples of flexible and brittle steel. Explain the actual difference between them. Explain the tempering of steel. 28. What is said of the annealing of glass? What of Prince Rupert's drops? What metals are the most malleable? What the most ductile? 29. What is said of the ductility of melted glass? What of the change of position of particles in making plates and wires of metals? What of welding? What is said of compressibility? What of the incompressiblity of liquids? 30. What influence has heat on the bulk of liquids? Illustrate by the thermometer. What is said of the compressibility of gases? How does elasticity operate in the case of the India-rubber ball? 31. Give the illustration in regard to jumping. State the experiment with the ivory ball. What is said of the movements of particles on each other in elastic substances? What of the degrees of elasticity in different substances? 32. What is the definition of elasticity? What is said of the usefulness of the variety of properties in matter? CHAPTER III. 33. What is meant by extension as a property of matter? Illustrate the fact that it is an essential quality. What is said of it in reference to air? 34. Does matter ever penetrate matter? Give the illustration represented in Fig. 6. Give that represented in Fig. 7. 35. State the arrangement of the diving-bell. Give the comparison between bullets and needles in relation to penetration. What is said of solution? What of odors? 36. What is the property of matter called inertia? Give illustrations of it. Illustrate the fact that matter has no power to stop its own motion. What is the reason that the popular notion is that matter is more inclined to rest than to motion? 37. What is said of perpetual motion? Why is it not true of divisibility that it is an essential property of matter? What is said of weight? CHAPTER IV. 38. What is said of the nature of attraction? What was Newton's idea of it? 39. What is said of attraction in solids? What of its different modes of action? What is the difference in attraction in the case of steel and of water? What is said of the freeness with which particles of a fluid move among each other? 40. Explain Fig. 9. Explain Fig. 10. 41. Give the difference between mercury and water in regard to the globular form. What if said of drops of water on leaves? 42. What is said of oil in reference to attraction? Describe and explain the manufacture of shot. What is said of the globular form of the earth and the heavenly bodies? 43. What is said of crystallization? State the examples cited. What is said of the crystallization of water? Give and explain the example of sudden crystallization. 44. What is said of frost-work? What of snow? 45. What is stated in regard to the snow-crystals of the arctic regions? What is said of order in nature? Why can you not make the surfaces of broken glass adhere? 46. Explain the cementing of glass. What is said of the adhesion of pieces of India-rubber? Describe and explain the experiment with bullets and with balls of lead. How may silver and gold be made to adhere to iron? What is said of the adhesion of tin and lead? What of the adhesion of panes of glass? 47. Upon what does the strength of adhesion depend? Illustrate the agency of heat in promoting adhesion. Give familiar examples of attraction between solids and liquids. Explain the experiment represented in Fig. 15. 48. What is said of stems in stagnant water? Explain Figs. 16, 17, and 18. 49. Explain Fig. 19. Explain the rise of fluids in tubes by Fig. 20. 50. What is meant by capillary attraction? Give familiar examples of the rising of liquids in interstices. 51. Describe and explain the process of getting out millstones. How does a blotter differ from writing-paper? CHAPTER V. 51. What is the attraction of cohesion? Give examples of attraction between masses or portions of matter. 52. Explain the falling of a stone to the ground. Illustrate the fact that attraction is mutual. Give the illustration of the ship and boat in full. 53. Illustrate the proportion between the mutual motions of the attracting bodies. Give the calculation in regard to the motion of the earth in attracting smaller bodies. 54. What is said of the universality of attraction? Explain the tides. What is said of the attraction of the moon for the land? What is the difference between the attraction of cohesion and the attraction of gravitation? Why is the word gravitation thus used? What is terrestrial gravitation? 55. Explain Fig. 22. Explain Fig. 23. What is said of substances suspended in different parts of the earth? 56. Explain Fig. 24. What is said of plumb-lines? 57. What is weight? Give the comparison in regard to muscular force. What is said of scales and weights? What of using springs in weighing? 58. What would be the effect on weight if the density of the earth were increased? In what ways would this be perceived? What is said of the variation of weight with distance? 59. What is said of the difference of weight on mountains and in valleys? What of weight in the moon? What of it in the sun? What is said of the different modes of attraction? 60. Show why attraction of cohesion seems to be different from gravitation. Show now that it is really not different. What is said of the experiment with the two bullets mentioned in § 66? What of the adhesion of liquids to solid substances? 61. What is said of the various results of attraction? Explain fully why you can pour water from a pitcher easier than from a tumbler. 62. Explain the operation of the quick movement by which you prevent water from running down the side of a tumbler in pouring it out. What is said of dropping from a vial? How is the size of drops limited? What is said of the movements of drops on window panes? 63. Why are the drops of different liquids different in size? Give the illustration about chalk. Give that about dust. Explain Figs. 27 and 28. 64. Explain Fig. 29. What is said of the difference in size between water and land animals? 65. Give the illustration in regard to trees. Give that in regard to mountains. What is said of the mountains of the moon? What of those of Jupiter? Give the illustrations in § 93 of transgression of the principles which have been elucidated. 66. What is the difference between the attraction treated of in natural philosophy and chemical attraction? CHAPTER VI. 67. Show what we mean by the centre of gravity by Figs. 30, 31, and 32. 68. Give the definition of centre of gravity, and explain it. What is shown by Fig. 33? 69. How can we find the centre of gravity of a body? What is said of scales and steelyards? 70. State what is represented by Fig. 38. Illustrate the fact that the centre of gravity seeks always the lowest point. 71. Give the illustrations of the rocking-horse, the swing, etc. What is said of the Laggan stones? Why does an egg lie on its side? 72. Give the illustrations from toys in § 101. Give the illustrations in § 102. 73. Upon what two things does the stability of a body depend? 74. What is said of the stability of bodies whose shapes are represented in Figs. 48, 49, and 50? What of that of a round ball? Why is the pyramid the firmest of all structures? 75. What is the relation of upright position to stability? What is stated of the tower of Pisa? 76. Give the familiar illustrations in § 105. What is said of the support of the centre of gravity in animals? 77. What is said of the skill exercised in walking? What of the mode of walking in a child? What of the motions of the centre of gravity in walking? 78. What is said of the walking of a man with wooden legs? Illustrate the management of the centre of gravity in different attitudes. Describe and explain the way in which one rises from a chair. 79. State and explain the wager case. What is said of unstable equilibrium? Give illustrations. CHAPTER VII. 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. 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 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? 106. What is stated about children in China? Why does the body of a drowned person sink? Why does it after a while rise? What is said about wading in rivers? 107. Explain the manner in which the specific gravity of a solid may be ascertained? Give the experiment of weighing water. What is stated of Archimedes and the crown? 108. Describe and explain the hydrometer. Relate the anecdote of the Chinese. What is said of the selling of milk in Switzerland? 109. What is said of the centre of gravity in floating bodies? Give the illustrations. 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. 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? 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 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? 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 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? CHAPTER XII. 194. What is sound? What relation has sound to rapidity of vibration? Mention cases in which the vibration of sounding bodies is manifest to the sight and touch. What is said of wind instruments? 195. State the analogy of a sounding body to a pendulum. Describe the process by which the sensation of sound is produced. Where does the vibration caused by the sounding body stop in the ear? What is transmitted from thence to the brain? 196. Give examples of the transmission of sound through various substances? State the experiment by which it is shown that sound is not transmitted through a vacuum. What is said of sound at great heights? 197. How far has the sound of a volcano been heard? If the same sound were made in space at that distance from the earth why could not the inhabitants hear it? What is the cause of the noise of bodies passing through the air? Why do the heavenly bodies, moving so rapidly, produce no sound? Cite examples showing the different velocities of sound in different media. 198. What is said of the uniformity of the velocity of sound? Show how we can measure distances by sound as compared with light in velocity. Upon what does the loudness of sound depend? Illustrate this point. 199. What is said of the diffusion of sound? What of its reflection? What of echoes? 200. What is said of multiplied and mingled reflections of sound? Explain the operation of whispering galleries by Fig. 187. 201. Explain the operation of the speaking-trumpet. Give other examples of the concentration of sonorous vibrations. 202. What is the difference between a musical sound and a noise? What is said of the exact regularity of musical vibrations? How are different notes produced in stringed instruments? Upon what does the note depend in wind-instruments? 203. Explain the operation of the organ-pipe represented in Fig. 190. What is said of the notes of bells and of musical glasses? Explain the mechanism of the human voice. 204. What is harmony? Upon what does it depend? Between what two notes of the scale is there the greatest harmony? What note next to the octave harmonizes best with the fundamental note? And what note next? Show why the second note, in contrast with the octave, is so discordant with the fundamental note. 205. State the proportions between the numbers of the vibrations in the different notes. If you know the number of vibrations of the fundamental note in a second, how may you determine the number of vibrations in the other notes? What is said of the number of notes in the diatonic scale? What of the proportionate lengths of strings for different notes? What is said of tuning instruments? 206. What is meant by saying that a note is too sharp or too flat? State in full what is said about the mysteries of sound and hearing. CHAPTER XII. 207. State the experiment of the three vessels, and the inference from it. 208. What other facts sustain this inference? How did Sir Humphrey Davy prove that there is heat in ice? What are the two theories of heat? What is the chief source of heat for the earth? What is said of the heat of the sun itself? 209. What is said of the universal influence of the heat of the sun in the earth? What of the heat supplied from within the earth itself? What of electricity as a source of heat? 210. What is said of chemical action as a source of heat? Give examples of the production of heat by mechanical action. What is said of the relations of heat and light? 211. Show the expansive influence of heat by describing the experiment represented in Fig. 192. Give familiar examples of this expansion. 212. How can you loosen a stopper stuck fast in a bottle? Give the anecdote about the Persia. Give the statement about the building in Paris. 213. What is said of the expansion of liquids by heat? How may the influence of this expansion upon specific gravity be shown? 214. What is said of thermometers? What of the invention of the thermometer? 215. State the plan of Fahrenheit's thermometer. Give the plans of other thermometers. 216. Why is Fahrenheit's thermometer, on the whole, the best? What is said of the expansion of gases by heat? State experiments in illustration. 217. What is said of balloons? What of the influence of heat on the atmosphere? Give examples of this influence. 218. Why, in heating apartments, do we have the heat created or introduced at as low a place as possible? Explain the draught of a chimney. Why does a stove-pipe generally draw better than a chimney? 219. State the experiment with the candle and the door. What is the explanation of the occurrence of wind? Explain the land-breeze. 220. Explain the sea-breeze. How are winds affected by the rotation of the earth? 221. Show by Fig. 201 why the prevailing winds at the equator are northeast and southeast. 222. Mention the melting points of various substances. What is said about the natural state of water and other substances? What are the two modes of changing a liquid into vapor? 223. What is said of the rapidity of evaporation? What of the solution of water in air? What influence has heat upon the capability of air to dissolve water? What phenomena illustrate this? How is it supposed that water rises in air? What fact is in opposition to this supposition? 224. What becomes of the water that rises in the air? What is said of the formation of fog and of clouds? Mention the different shapes of clouds and their names. 226. What is said of the influences that give shape to clouds? 228. State how rain is produced, and explain Fig. 208. How are snow and hail formed? What is said of vaporization? 229. What influence has pressure upon the formation of vapor? Give the experiment with ether in illustration. Describe the experiment represented in Fig. 209. What is said of Papin's digester? 230. What is said of steam? In what consists the power of the steam-engine? How is the expansive force of the steam in the boiler estimated? Describe the working of the engine by Fig. 210. 231. What is the difference between high and low pressure engines? What is said of the communication of heat? How many modes of communication are there, and what are they? What is the mode called convection? 232. Give examples of convection. What is the conduction of heat? 233. State the experiment represented in Fig. 211. State the experiment represented in Fig. 212. What is said of non-conductors of heat? Give the examples cited. 234. Explain Davy's safety-lamp. 235. Give what is stated in the note about Stephenson and Davy. What is said of the influence of density on the conduction of heat? Give the illustration about melting snow. 236. State the experiments which show that liquids are poor conductors of heat. What is said of air as a non-conductor of heat? What is said of double windows? 237. What is said of arrangements of the walls of buildings? What of an arrangements for preventing the spreading of fires in blocks? 238. How are animals in very cold regions protected from the cold? What is it in their coverings that affords the protection? What is said of the coverings of quadrupeds that are natives of warm climates? What of the elephants whose remains are found in Siberia? 239. What changes take place in the coverings of animals carried from a cold to a warm climate, and the reverse? Why has man no covering against the cold? Explain the object of clothing. What is said of articles of clothing? What of loose clothing? What of coatings of straw put on trees? What of bricks compared with stones? 240. What is said of cocoons? What of buds of plants in winter? What of snow as a protection of plants? 241. State the arrangement of snow observed in the arctic regions. State in full what is said of the influence of the conduction of heat upon sensation. 242. What is meant by the radiation of heat? Give examples of it. What is said of the connection of heat and light in the rays of the sun? What is said of heat from a common fire? 243. What is said of the relation between absorption and radiation? What of the reflection of heat? State the experiment with the mirrors and the thermometer and flask. 244. Explain the experiment with the ice. Give the experiment with phosphorus. Give the experiment represented in Fig. 218. 245. Explain the formation of dew. State the analogy of the tumbler. What is said of the circumstances that influence the deposition of dew and frost? 246. What is said of different substances in regard to the deposition of dew? What about Gideon's fleece? What is the dew-point? How can you ascertain in it? 247. What is said of the freezing of mercury? Explain the difference between sensible and latent heat. What is said of capacity for heat? State the experiment represented in Fig. 219. 248. What is the relation of heat to density? Give the illustrations. 249. What is the reason that the air is so cold on great heights? What is the relation of heat to the forms of substances? What is said of the melting of ice? What of the vaporization of water? State the general conclusion in regard to latent and sensible heat. 250. State in full what is said of latent heat in reference to clouds. Explain the operation of freezing mixtures. 251. State the examples of the production of cold by evaporation. 252. State and explain the experiment represented in Fig. 221. 253. Give the facts stated in regard to the degree of heat which man can endure. Give the reasons why the heat did not produce a greater effect in these cases. 254. What effect does heat produce upon the bulk of substances? What is said of water as an exception? Describe the process of freezing as illustrated by the diagram. 256. What would be the process if the exception did not exist? State what would be the results. 257. What would be the consequence if the freezing point were above 32°? What if it were below? What is said of the force of expansion in ice? What are some of the benefits which come from this expansion? CHAPTER XIV. 258. What is Newton's theory of light? What is the undulatory theory? State the analogies to sound and heat. When is a body luminous? What are the sources of light? 259. How may you see that light moves in straight lines? State various familiar recognitions of this fact. Illustrate the fact that the intensity of light is inversely as the square of the distance. 260. What is said of the velocity of light in regard to ordinary distances? How long is light coming from the sun to the earth? What is said of the light coming to us from certain stars? 261. Give the observation of Roemer represented in Fig. 226. 262. What is said of the reflection of light? What of its reflection in relation to seeing? What of the images formed in mirrors? 263. Show by Fig. 228 why the image in a mirror seems to be as the same distance behind it that the object is before it. Explain by Fig. 229 the operation of the kaleidoscope. 264. Explain the operation of a concave mirror by Fig. 230. Explain that of a convex mirror by Fig. 231. 265. What is meant by the refraction of light? Illustrate its reflection in passing from a denser into a rarer medium. Then from a rarer into a denser. 266. How is the refraction in regard to a perpendicular in the two cases? Explain dawn and twilight. Explain what is represented in Fig. 234. 267. What are mirages? Describe the mirage which occurred at 268. What is said of mirages in deserts? 269. Describe the mirage of the French coast. Explain what is meant by the visual angle as illustrated by Fig. 236. 270. Explain Fig. 237. What are lenses? What are the different kinds? 271. What is the difference of effect in convex and concave lenses? Explain the effect of a convex lens on the visual angle. What is said of microscopes and telescopes? 272. Describe and explain the magic lantern. Describe and explain the camera obscura. 273. Describe the arrangement of a camera for sketching. How is the eye like a camera? 274. Describe the arrangement of the parts of the eye as mapped in Fig. 244. 275. Show now particularly how the eye is like a camera. What is said of the influence of the cornea on the light? Show what is required for distinct vision, as illustrated in Fig. 245. Show why it is that objects brought very near the eye are not seen distinctly. 276. What is said of the microscope? Explain the difficulty in the near-sighted. In the far-sighted. 277. How can you show that the images of objects in the retina are inverted? Give in full what is said of explanations of the fact that we see objects erect notwithstanding this inversion. Explain single vision. 278. By what simple experiment can you show the explanation of single vision to be correct? What is said of squinting? Explain the stereoscope. 279. What is said of distinct impressions on the retina? Explain the thaumatrope. 280. State in full what is said of the compound nature of light. Give the proportions of the colors in it. What is said about there being only three colors? 281. What is said of the recomposition of decomposed light? Give the illustration of the powder—the circular board—the top. 282. What is said of the colors of substances? What of the variations of these colors in different lights? What of variations with varying positions? What of the colors of clouds? 283. Explain the formation of the first rainbow by Fig. 253. Explain the formation of the second bow by Fig. 254. 284. What is said of the circumstances under which rainbows are seen? 285. Explain in full the formation of the two bows as illustrated by Fig. 255. What is said of the bow as seen by different persons, and at different moments by the same person? What of rainbow hues in dew-drops and ice-crystals? 286. Give the dissection of light as represented in Fig. 256. What is said of Daguerreotyping? CHAPTER XV. 287. What is the origin of the term electricity? What is said of attraction and repulsion in electricity? 288. What is the supposed explanation of electrical repulsion? Explain the difference between resinous and vitreous electricity. What is said of the two supposed electrical fluids? Detail the illustrations of attraction which are stated. 289. State the theory of Franklin. Explain the use of the terms positive and negative. Illustrate the fact that the kind of electricity excited depends on what a substance is rubbed with. 290. What is said of the incorrectness of the terms vitreous and resinous? What is said of conductors and non-conductors? Why are non-conductors called insulators? 291. What marked difference is there between heat and electricity? State the experiment represented in Fig. 258. What is said of electrics and non-electrics? 292. What is said of equilibrium in electricity, and of its disturbance? Give in full what is said of the universality of electricity. 293. State what is said of induction, as illustrated by the experiment represented in Fig. 259. 294. State the experiment represented in Fig. 260. Describe the arrangement and operation of the electrical machine represented in Fig. 261. 295. Describe the cylinder machine. State the experiment with the pith balls. State that with the head of hair. 296. State the experiment with the tissue-paper. State that with the dancing figures. State that with the bells. 297. Describe the experiment with the tin-foil. Describe the insulating stool and the operation of it. 298. What is said of the escape of electricity from points? Describe the apparatus represented in Fig. 269, and the operation of it. What is said of the discharge of electricity from a point in a dark room? Describe the Leyden jar. 299. Explain the operation of the Leyden jar. What would be the effect of connecting the inside foil with the outer by a strip of foil? Give in full the experiment represented in Fig. 272, and the explanation. 300. What is said of the discharge of the jar? How can a large number of persons take a shock from it together? 301. Explain the effect of moisture upon the charged jar. State the experiment represented in Fig. 274. 302. What is the electrical battery? What is said of the light produced by electricity? 303. To what is the report of electricity owing? What is said of mechanical injuries caused by electricity? What of the heat caused by it? What effects may be produced by this heat? 304. What was the discovery of Franklin, and how did he make it? 305. Relate the accident which occurred at St. Petersburg. What is said of lightning-rods? 306. What was Sulzer's experiment? What were Galvani's observations? 307. What is said of the pile of Volta? What of his cup battery and of other batteries? 308. What difference is there between frictional and voltaic electricity? CHAPTER XVI. 308. What are loadstones? Where do they abound? What is said of discoveries in magnetism? Whence come the terms magnetism and magnet? 309. What is said of the attraction of magnetism? What law is there in regard to it? What is said of the poles of a magnet? What of magnetism by induction? 310. What is said of attraction and repulsion in magnets? Explain the formation of the curves of iron filings in the experiment represented in Fig. 282. 311. How may artificial magnets be made? What is said of the horseshoe magnet and its armature? 312. What is said of the magnetic needle and the mariner's compass? 313. What is the declination of the needle? When was it first observed? What is said of observations after this? What is said of the dip of the needle? 314. What is said of the earth as a magnet? What of it as a magnetizer? 315. What is said of fixing magnetism? What of impairing it? In what other substances besides iron does magnetism exist? In what is magnetism like electricity? In what is it unlike it? 316. What relation has magnetism to electricity? What were the original observations of Oersted in regard to it? 317. Describe the manner of making the most powerful electro-magnets. Describe the experiment represented in Fig. 287. 318. Show the application of electro-magnetism in the electric telegraph. 319. What is the contrivance called the signal key? How is the alphabet of Morse's Telegraph constructed? 320. What is said of the communication through the earth in telegraphing?
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