CONTENTS. 



III. TELEGRAPHS BY GALVANIC ELECTRICITY. 



Page 



19. Discovery of Galvanism 13 



20. Yolta's Contact Theory Chemical Theory ...... 16 



21. Volta's Pile 17 



22. Properties of the Voltaic Pile , . . . 17 



23. Decomposition of Water 18 



21. Sommering's Telegraph . 18 



25. Schweiger's Telegraph 20 



26. Coxe's Telegraph .^ ...... 20 



IV. TELEGRAPHS BY ELECTRO-MAGNETISM AND MAGNETO- 

 ELECTRICITY. 



27. Oersted's Discovery of Electro-Magnetism 21 



28. Schweiger's Multiplier 22 



29. Ampere's Telegraph . . . ..-'^-.i VI ..,.-.. 22 



30. Eitchie's Telegraph . . . . . 23 



31. Sturgeon's Discovery of the Electro-magnet ...... 24 



32. Schilling's Telegraph * . . . 25 



33. Volta-Electric Induction and Magneto-Electricity ... 25 



34. Gauss and Weber's Telegraph . . . . .','..'.. 27 



35. Steinheil's Telegraph .............. 32 



36. Earth Circuit ...'".. . . 35 



37. Wheatstone's Telegraph . . .:....,..,.,:...;. 36 



38. ,, Alarm . . ... . ._,;...;. .... 38 



39. Eelay ............... 40 



40. Morse's Early Telegraph . . ... .,* ..,;. . . . 40 



41. ,, Electro-Magnetic Telegraph . . ... . .., ;. 41 



42. ,, Eelay . . ;..,..- ... ^ .: ; , .... . . . 42 



43. Davy's Telegraph .. . . . 42 



44. Wheatstone's Dial Telegraphs with Battery 43 



45. ,, ,, Improved .... 45 



46. ,, ,, Magneto-Electricity . 45 



V. TELEGRAPHS NOW IN USE. 



47. Cooke and Wheatstone's Single Needle Instrument . . 46 



48. ,, ,, Double ,, , , . 50 



49. Siemens' Self-acting Make-and- Break . . . '..'.... 51 



50. House's Printing Telegraph . . . . . . ." . . . 53 



61. Hughes' Eoman-type-printing Telegraph 55 



52. Breguet's Electro-Magnetic Dial Instrument .... 65 



53. Kramer's Pointer Telegraph 70 



54. ,, Alarm Circuits 72 



55. Siemens and Halske's Magneto -Electric Pointer Telegraph 75 



56. ,, ,, Polarised Alarm . . 79 



