G6S 



MINES, MILITARY. 



MINIATURE. 



666 



1. Used for the descent of ditches and passage of cannon. 



2. Used for the passage of troops, two deep. 



3. Ordinarily employed for general purposes of attack, giving the 

 miner room to work easily either on both or one knee, and is the most 

 rapidly executed. 



4 & 5. Employed for short distances, about 10 or 12 feet only, for 

 placing charges, &c., as being more easily tamped. 



When cases are used, mines can be driven at nearly twice the rate 

 that they can with frames and sheeting : namely, great galleries and 

 shafts about 1 foot an hour, common galleries about 14 feet an hour. 



Ventilation requires to be well looked after in mines, for not only do 

 the gases generated by the explosions of powder collect in the 

 descending and ascending portions of galleries and often stifle the miner, 

 but even under ordinary circumstances the air is so vitiated by respi- 

 ration that a branch cannot safely be driven more than 60 feet. Hence 

 openings should be made to the surface of the ground, and, if possible, 

 concealed from the enemy, and communications made from adjacent 

 galleries to create a draught. It also often becomes necessary to use 

 artificial means of forcing air down into a mine, by means of a blower or 

 bellows and metal pipes carried to the end of the mine. 



The chamber in which the powder is placed is a cubical excavation 

 formed on one side of the gallery, very little larger than is necessary to 

 enable it to receive the box which contains the powder. When this is 

 deposited, the vertical face of the chamber is covered with boards, 

 which are kept in their places by short timbers fixed in horizontal 

 positions between them and the opposite side of the gallery. The 

 latter is then filled up with earth, well rammed, to an extent in the 

 length of the gallery greater than that of what is called the line of 

 least resistance ; that is, a line imagined to be drawn from the chamber 

 perpendicularly to the nearest surface where the crater would be 

 formed. The mass of earth thus filling the gallery is called the tamping 

 of the mine. A train of powder in a canvas hose, forming a tube about 

 three-quarters of an inch in diameter, and for security contained in a 

 wooden trough called an auyet, or a casing-tube, is laid from the box in 

 the chamber through the tamping to the place where the fire is 

 to be applied; to its extremity is attached a piece of port-fire, 

 which, being lighted, the fire communicates by means of the hose 

 with the powder hi the chamber, and an explosion takes place. Mines 

 are also fired by means of what is called Bickford's fuse, which con- 

 sists of powder encased in a kind of rope made of spun yarn, tarred. 

 This fuse is waterproof, and not so liable to be accidentally ignited, 

 and is especially adapted for damp ground. Electricity is also now 

 constantly employed in firing mines. It was used by the Russians hi 

 then- mines at Sebastopol, and by the English in the demolition of the 

 docks, &c. 



The dimensions of the crater or funnel formed by the explosion 

 depend on the amount of the charge ; its form may be considered as 

 an irregular frustum of a cone, or paraboloid, and the mine is denomi- 

 nated one-lined, tico-lined, &c., according as the diameter of the crater 

 at the surface of the ground is equal to once, twice, &c., the length of 

 the line of least resistance. Every explosion of this kind necessarily 

 produces a compression of the earth in all directions about the chamber 

 to a certain extent; and the mines formed with high charges have been 

 denominated globes of compression from this circumstance. A line 

 drawn from the chamber to the circumference of the crater, on the 

 ground, is considered as the radius of the globe of compression. 



The last mentioned description of mine was first employed by Belidor 

 for the purpose of destroying the galleries of the besieger at distances 

 far greater than had before been considered practicable. When 

 a very small, or at least, comparatively to its depth, a very small mine is 

 exploded, no crater is produced, but it is evident that the earth about 

 must be compressed, and galleries, &c., destroyed to a certain distance : 

 the radius of this sphere of compression is termed the radius of rupture. 

 When a crater is produced, the solid compressed will no longer be a 



r'ieroid, but an elipsoid, or nearly so, with its major axis passing 

 ough the centre of the charge, at right angles to the line of 

 least resistance. With overcharged mines this radius of rupture 

 in greatly increased : in fact it is found that with the ordinary 

 or two-lined crater the radius of rupture, or semi-major axis of 

 the ellipsoid, is 1'7 tunes the line of least resistance ; and the semi- 

 minor axis, or extent of compression downwards, is 1'3 times the line 

 of least resistance. With a globe of compression producing a six-lined 

 ciater or maximum charged mine, these lines are 4'36 and 1'4 times the 

 lino of least resistance. It will be seen that the lateral effect increases 

 much more than the downward effect, as might be imagined. This 

 great lateral effect was employed by Belidor for destroying the 

 galleries of the besieger : such mines are, from the circumstances of 

 the respective cases, perhaps more applicable by the besieger than 

 the besieged. 



The rules for determining the charges of mines are founded on the 

 resultD of experiment, and it is evident that the charges must vary both 

 with the nature of the soil and with the proposed figure of the mine, 

 that is, with the ratio between the diameter of the crater and the length 

 of the line of least resistance. When a mine of the kind called two- 

 lini-il i formed in common earth, the amount of the charge in pounds 

 is considered as very nearly equal to one-tenth of the cube of the line 

 of least resistance in feet; but for a three-lined and a four-lined mine 

 it U supposed that the cube of this line should be multiplied by '21 



and by '45 respectively. It is said that Belidor, somewhere about the 

 years 1758 to 1762, fired three charges of 3600 Ibs., at a depth of 

 12 feet, all of which produced craters of 36 feet radivis, or six-lined 

 craters. In an experiment made at Potsdam, when a four-lined mine 

 was formed in a sandy soil by the Prussian Major Le Febvre, the cube 

 of the line of least resistance in feet was very nearly equal to he charge 

 in pounds. According to the latest experiments of the French engineers, 

 the charges of powder necessary to remove one cubic yard (English) of 

 material are as follows : 



Common earth 

 Strong sand 

 Potters' clay . 

 Loose sand 

 Old masonry . 

 Freestone . 



1'21 pounds (English) 



1-64 



1-75 



1-85 



1-94 



2-14 



Now the figure of the crater being supposed to be a paraboloid, of 

 which the centre of the chamber is the focus if a be the length of the 

 line of least resistance in yards, and n a represent the radius of the 

 crater at the surface of the ground, also if T= 3'1416, we shall have 



for the volume of the crater in cubic yards ; therefore, multiplying 

 this volume by the numbers in the above table, we should have the 

 charge in pounds, which will hold good for mines up to three-lined 

 craters. 



The following rules, given by General Sir Charles Pasley, are very 

 valuable, as deduced from experiment. L.L.R. meaning line of leaat 

 resistance. 



CHARGES AND EFFECTS PRODUCED IN MIXED EARTH. 



In order to determine the proper size of the chamber, or rather of 

 the box, which is to contain the powder, it will be necessary to 

 observe that one pound of gunpowder occupies, in volume, abou t 

 30 cubic inches. 



Experience has shown that the greater the charge of powder, the 

 greater is the quantity of earth removed by the explosion. But this 

 fact has ite limits ; for when the charge is considerable, since the whole 

 of the powder does not take fire instantaneously, it will happen that 

 the earth is partially displaced before the inflammation is complete 

 so that fissures being formed in the ground, the force of the powder is 

 spent in the air without producing any effect. Hence it may be con- 

 cluded that there is a certain charge of powder which will produce a 

 maximum of effect ; and it is supposed by Belidor that, in earth of 

 mean tenacity, the greatest craters will have their diameters, at the 

 surface of the ground, equal to about six times the length of the line 

 of least resistance. 



MINIATURE. The term miniature would apply with equal 

 propriety to every kind of painting executed on a minute or diminutive 

 scale ; but as commonly employed it includes only two, though some- 

 what widely different, kinds of painting. One of these is that style of 

 ornamental painting, or illuminating, which is seen in its greatest 

 perfection on the vellum pages of mediaeval bibles, psalters, service- 

 books, and other costly manuscripts : the other kind is that of small 

 portraits executed chiefly on ivory, to which indeed the term has in 

 ts popular acceptation been of late years almost exclusively confined. 



