vi CONTENTS. 



PAGE 



21. Singular displacement at Riobamba. 22. Earthquakes are 

 not generally attended by any peculiar atmospheric prognostics. 

 23. Earthquakes most frequent at the equinoxes. 24. Well 

 described by Pliny and Seneca. 25. Attended by subterranean 

 thunder. 26. Character of these sounds. 27. Are heard at 

 great distances from the place of the earthquake. 28. Examples 

 of this. 29. Subterranean roaring of Guanxauato. 30. Their 

 effects on the inhabitants 31. Great extent over which earth- 

 quakes spread. 32. They affect the bottom of the ocean. 33. 

 Curious examples of these effects . . . . . .145 



CHAP. II. 34. Earthquakes at Jamaica. 35. Extent of the Lisbon 

 earthquake. 36. Long continuance of slight earthquakes. 

 37. They affect all kinds of strata. 38. They sometimes pass 

 over certain districts called bridges. 39. Inferior strata are 

 sometimes agitated when the superficial strata are undisturbed. 

 40. Inferior strata sometimes undisturbed when superficial strata 

 are agitated. 41. Undulations often, but not always, move 

 parallel to mountain chains. 42. Humboldt's description of the 

 effects of earthquakes. 43. Number of earthquake-shocks in 

 England. 44. Ejection of matter from the interior of the earth. 

 45. Temperature of water in Artesian wells. 46. Temperature 

 indicates depth. 47. Natural thermal springs. 48. Independent 

 of strata. 49. Their occasional permanency the classic fountains 

 still flow. 50. From certain depths vapour only rises. 51. 

 Also certain gases Artesian fire- wells. 52. Carbonic acid its 

 effects in former states of the globe origin of coal beds. 53. 

 And marbles. 54. Mud volcanoes. 55. Those of remote origin. 

 56. Progressive development. 57. Formation of dome-shaped 

 mountains. 58. Crater of elevation. 59. Active volcanoes. 

 60. Successive stages of their formation. 61. Not uniformly or 

 permanently active. 62. Intervals of activity and repose. 63. 

 Dependent on the height. 64. Stromboli. 65. Guacamayo. 

 66. Volcanoes of the Andes. 67. Exceptions explained. 68. 

 Eruptions often lateral. 69. Groups of small cones. 70. Re- 

 markable spectacle of Cotopaxi. 71. View of an active crater. 

 72. Eemarkable permanence of the form of craters. 73. Effects 

 of snow-capped cones. 74. Cause of the fiery appearance of 

 ejected matter. 75. Islands of volcanic origin. 76. Volcanic 

 theories 161 



THE BAROMETER. 



1. Origin of the name. 2. Conditions necessary to render the instru- 

 ment useful. 3. To purify the mercury. 4. To cleanse the tube. 

 5. To fill the tube. 6. To invert it in the cistern. 7. Con- 

 struction of a barometer. 8. Effect of temperature on the 

 barometric column. 9. To ascertain if the vacuum above the 

 column be perfect. 10. Expedients to render minute variations 

 of altitude visible. 11. Diagonal barometer. 12. Wheel 

 barometer. 13. Common siphon barometer. 14. Use of the 



