[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. [23] Capt. Schaw’s (R. E.) rule for an untamped charge of gunpowder placed as above described is _C_ lbs. = ⅔ L. L. R.^2 × _B_, in which _C_ = charge in pounds, _B_ = breadth of bridge in feet, and L. L. R. = line of least resistance in feet, measured through the arch. [Transcriber’s Note: Obvious printer errors corrected silently. Inconsistent spelling and hyphenation are as in the original.] End of Project Gutenberg's Attack of Fortified Places., by James Mercur