vi CONTENTS. 



PAGE 



great magnitude. 14. Their rapid changes. 15. Hypotheses to 

 explain them. 16. They are excavations in the luminous 

 coating. 17. Their prevalence varies. 18. Observations upon 

 them. 19. Their dimensions. 20. Facules and Lucules. 21. 

 Physical state of the Solar surface. 22. Luminous coating is 

 gaseous. 23. Gaseous atmosphere outside it. 24. Effects of 

 such an atmosphere on radiation. 25. Hypothesis of Sir J. 

 Herschel. 26. Intensity of heat at Sun's surface. 27. 

 Supposed source of heat 97 



THE ELECTRIC TELEGRAPH. 



CHAP. I. 1. Subjugation of the powers of nature to human uses. 

 2. Locomotion twenty years since. 3. Circulation of intelligence 

 then. 4. Supposed prediction of succeeding improvements 

 Railway locomotion. 5. Electric telegraphy. 6. Fabrication of 

 diamonds sun-pictures gas-lighting electro-metallurgy. 7. 

 Such predictions would have been deemed incredible. 8. Electro- 

 telegraphy the most incredible of all. 9. Remarkable experiment 

 by Messrs. Leverrier and Lardner. 10. Velocity of electric 

 current. 11. No limit to the celerity of telegraphy. 12. 

 Physical character of electricity. 13. Not essential to the 

 explanation of electro-telegraphy. 14. Electricity a subtle fluid. 

 15. Properties available for telegraphy. 16. Voltaic battery. 

 17. It is to the electric telegraph what the boiler is to the 

 steam-engine. 18. Means of transmitting the fluid in required 

 directions. 19. Conductors and insulators. 20. Conducting 

 wires. 21. Voltaic battery. 22. Transmission and suspension 

 of the current. 23. Current established by earth contact. 

 24. Theories of earth contact. 25. The return of the current 

 through the earth. 26. Various bodies evolve electricity. 

 27. Common plate battery of zinc and copper. 28. Why zinc 

 and copper are preferred. 29. Charcoal substituted for copper. 

 30. Elements not essential. 31. Various chemical solutions 

 used. 32. Daniel's constant battery. 33. Same modified by 

 Pouillet. 34. Grove's and Bunsen's batteries. 35. Necessary 

 to combine many elements 113 



CHAP. II. 36. Common plate battery. 37. Combination of 

 currents. 38. Loss of intensity by imperfect conduction. 39. 

 Cylindrical batteries. 40. Pairs, elements, and poles defined. 

 41. Origin of term voltaic pile. 42. Use of sand in charging 

 batteries. 43. To vary intensity of current. 44. Batteries used 

 for English telegraphs. 45. Amalgamating the zinc plates. 46. 

 The line-wires, material and thickness. 47. Objection to iron 

 wires. 48. Manner of carrying wires on posts. 49. Good 

 insulation. 50. Expedients for obtaining it. 51. Forms of 

 insulating supports. 52. Dimensions and preparations of the 

 posts. 53. Forms of support used in England. 54. Winding 

 posts. 55. Supports in France. 56. In America. 57. In 

 Germany. 58. Wire insulated by superficial oxydation. 59. 

 Leakage of the electric fluid by the conduction of the atmosphere. 



