CONTENTS. v 



PAGE 



meridian. 36. Dimensions of the terrestrial spheroid. 37. Its 

 departure from an exact globe very small. 38. Its density and 

 mass. 39. Determined by Cavendish and Maskelyne. 40. Its 

 total weight. 49 



TERRESTRIAL HEAT. 



CHAP. I. 1. Heat an important agent. 2. Its local variations. 

 3. Diurnal period. 4. Annual period. 5. Mean diurnal 

 temperature. 6. Mean monthly temperature. 7. Mean annual 

 temperature. 8. Temperature of a place. 9. Isothermal lines. 

 10. Isothermal zones. 11. Thermal equator. 12. Second 

 isothermal zone. 13. Third. 14. Fourth. 15. Fifth and 

 Sixth. 16. Polar regions. 17. Climate varies on the same 

 isothermal line. 18. Constant, variable, and extreme climates. 

 19. Classification of climates. 20. Extreme temperature in 

 torrid and frigid zones/ 21. Elevation affects temperature. 

 22. Snow line. 23. Thermal conditions below the surface. 

 24. Stratum of invariable temperature. 25. Varies with the 

 latitude. 26. Its form. 27. Conditions above it. 28. Con- 

 ditions below it. 2 9 . Temperature of springs. 30. Temperature 

 of greatest density of water. 31. Thermal condition of seas and 

 lakes. 32. Thermal condition of a frozen sea. 33. Process of 

 thawing. 34. Depth of stratum of constant temperature. 35. 

 Superficial agitation extends only to a small depth. 36. Great 

 utility of the state of maximum density. 37. Variations of 

 temperature of the air. 38. Interchange of Equatorial and 

 Polar waters. 39. Polar ice. 40. Ice-fields. 41. Icebergs. 

 42. Their forms and magnitude. 43. Sunken icebergs. 44. 

 Curious effects of their superficial fusion. 45. Depth of Polar 

 Seas. 46. Cold of Polar regions 65 



CHAP. II. 47. Sources of external heat. 48. Solar heat. 49. Its 

 quantity ascertained. 50. Heat at sun's surface. 51. Tempe- 

 rature of celestial spaces. 52. Quantity of heat supplied by 

 them. 53. Summary of heat supplied. 54. Winds. 55. 

 Produced by rarefaction and compression. 56. Sudden con- 

 densation of vapour. 57. Hurricanes. 58. Their cause. 

 59. Waterspouts. 60. Evaporation. 61. Saturation of air. 

 62. May arise from intermixing strata. 63. Effect of pressure. 

 64. Dew. 65. Hoar frost. 66. Artificial ice. 67. Fogs and 

 clouds. 68. Rain. 69. Its quantity. 70. Snow. 71. Hail. 

 72. Hailstones. 73. Extraordinary hailstones . . . .81 



THE SUN. 



1. An object of great interest. 2. Its distance. 3. Magnitude. 

 4. Illustrations. 5. Its volume. 6. Mass or weight. 7. 

 How ascertained. 8. Application of this principle. 9. Its 

 density. 10. Form and rotation. 11. Determined by the 

 appearance of spots. 12. Discovery of Solar spots. 13. Their 



