TERRESTRIAL HEAT. 



CHAPTER I. 



Heat an important agent. 2. Its local variations. 3. Diurnal 

 period. 4. Annual period. 5. Mean diurnal temperature. 6. 

 Mean mouthly 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. 

 Conditions below it. 29. Temperature of springs. 30. Temperature 

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

 LARDKER'S MUSEUM OP SCIENCE. v 65 



No. 32. 



