40. A Wet Ditch without Current, 38 41. A Wet Ditch with Current, 40 CHAPTER IV. BATTERIES, OBSERVATORIES, AND MAGAZINES. 42. Batteries Defined, etc., 42 43. General Requirements of Siege-batteries, 42 44. Construction of Batteries for Field-guns, 43 45. Batteries for Siege-guns and Howitzers, Elevated and Sunken,--General Considerations, 44 46. Screens, 45 47. Exposed Sunken Battery, 46 48. Tracing the Battery, 47 49. Constructing the Central Passage and Splinter-proof, 48 50. Constructing the Battery, 49 51. Alternative Construction, 50 52. Splinter-proofs (additional), 50 53. Sunken Battery in a Parallel, 51 54. Battery behind Crest of a Hill, 53 55. Batteries on Sloping Ground, 53 56. Embrasures, 53 57. Observatories, 54 58. Drainage, 55 59. Mortar-batteries, 55 60. Magazines, 57 61. Cover for Magazines, 58 62. Location of Magazines, 58 63. Construction of a Magazine subject to Direct Fire only, 60 64. Manner of Executing the Work, 61 65. Mined Magazines, 61 66. Elevated Magazines, 62 67. Precautions against Dampness, 63 CHAPTER V. SIEGE OPERATIONS. 68. The Attack--Successive Steps, 64 69. The First Period, 65 70. The Investment, 65 71. Bringing Up and Posting the Besieging Force, 67 72. Fortifying the Camps, Parks, etc., 68 73. Distance of the Line of Investment from the Works, 70 74. Strength and Composition of the Besieging Force, 70 75. The Point of Attack, 73 76. First Artillery Position, 75 77. Opening Fire, 76 78. Plan of Attack, 78