1 In the siege of Strasburg, 1870, a bridge of beer casks was built across the ditch of Lunette No. 52, between nightfall and 10 P. M., September 21st. The ditch was about 66 feet wide and 9 to 10 feet deep. This bridge gave access to the lunette. It was subsequently sunk by the fire of the work and was replaced by a causeway.—Franco-German War, Official Account, Part 2, vol. 1., pp. 88, 89.

2 One of a group of trees may frequently serve for this purpose.

3 The charge for the 5" siege gun is 15 lbs. of powder; 200 rounds = 3,000 lbs.; 2 guns, 6,000 lbs.

4 No special box has been adopted in our service. The English box is 1' 9" × 1' 5½" × 1' 5" outside, metal lined, and holds almost 100 lbs. of made-up cartridges.

5 The crater radius of a mine with L. L. R. of 6' to 12' and a charge of 6,000 lbs. of powder would be about 44 feet (Art. 7, Military Mining). The radius of the mound of earth thrown out would probably be three times this.

6 Quoted from Mahan’s Siege Operations.

7 A shell from a 9" .45 rifled mortar has in experimental firing produced in moderately hard ground a crater 8 feet deep and 19½ feet in diameter.

8 From the unpublished records of three experimental mines fired at Willet’s Point in 1877-83 it would seem that the quantities given in this table are greater than those required if good American powder is used. These mines, in a soil of modified drift, used. These mines, in a soil of modified drift,
with a L. L. R. of 12 ft. required 1.02 lbs. per cu. yd. = 1 lb. ? oz.; and
with a L. L. R. of 17 ft. required 1.15 lbs. per cu. yd. = 1 lb. 2½ oz.

9 Six-lined craters (r = 3l) are generally considered as the practical limit of overcharged mines, although at Chatham mines have been fired giving r = (3¾)l. The published data concerning them indicate that they required charges larger than the formulas above given call for.

10 Describe the semicircle BMNF. Then

11 General Abbot’s experiments in submarine mining fix the relative values of cannon powder and dynamite No. 1 in water, measured by the pressure exerted by them (not by the craters formed), as 1 : 2.45. The characters of the media and the explosives would naturally lead to the inference that the superiority of dynamite over powder would be greater in water than in earth.—J. M.

12 The 82 lb. dynamite-mine at Willet’s Point produced almost exactly the same effect upon the gallery of access as the 200-lb. cannon-powder mine, while its external crater was considerably less in diameter. Its crater was surrounded, however, by concentric cracks spaced at intervals of 3 or 4 feet to a distance of about 40 feet from the centre of the crater. No such effect was produced by the powder-mine.

On the other hand, the actual radii of rupture produced by five experimental mines fired at Olmutz in 1871-2 agree very closely with the values which result from applying Lebrun’s formulas to craters of the same size and shape produced by gunpowder, and indicate that charges of dynamite and gunpowder which produce identical craters will also have identical radii of rupture. The somewhat contradictory results given by the Willet’s Point and Olmutz mines show the necessity for further experiments.

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.

23 Capt. Schaw’s (R. E.) rule for an untamped charge of gunpowder placed as above described is C lbs. = ? 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.