[13] To pass a 5" siege-gun, mounted upon a high or “overbank” carriage (model 1887), requires a gallery 7' × 7' in clear.
[14] Four of these may be unskilled laborers.
[15] No. required at commencement of gallery. Beyond 4 feet add one man, and one additional for every 20 feet of gallery.
[16] Instead of a truck a canvas bag may be used. A large hoe or drag may be used to draw back the earth from the face of the gallery.
[17] One mason’s level.
[18] These numbers are for small shafts of about 2' by 4'; large shafts require a larger force. They advance at about the same rate as galleries of equal cross-section.
[19] In the blasting at Hell Gate, 1870-76, several cases occurred, both with nitro-glycerine and compressed gun-cotton, in which a part of the charge exploded, breaking the blast-hole nearly to the bottom, and leaving the remainder of the charge unexploded in the bottom of the hole, from which it was subsequently recovered. Similar results were obtained in experiments, conducted by Capt. (now Major) Heuer, 1875-6, with long tubes filled with nitro-glycerine. See also Encyc. Brit., vol. xvi, “Mining,” for similar information.
[20] In compact soil the sound of a pick can be heard up to about 40 feet, and at about 20 feet when the miners are working as quietly as possible.
[21] E.g., the sieges of Candia (1667-9), Schweidnitz (1762), Silistria and Brailow (1828-9), Sebastopol (1854-5), Vicksburg (1863), Petersburg (1864), etc., etc., and the experimental mining operations at Graudenz in 1862. See Woolwich and Chatham Text-books, Mahan’s Field Fortifications, Guerre de Siège Blanchecotte et Chauvot Fontainebleau, etc., etc.
[22] A dynamite cartridge 1" in diameter weighs ½ lb. per running foot; 2" in diameter, 2 lbs. per ft.; etc.