Page:Cyclopaedia, Chambers - Volume 2.djvu/200

 MIN

always run eirher horizontal or oblique; and for that Rea- fon, are eaiicft found on the fides of Eminences.

The Metallic Veins are commonly encompaffed with a fort of Stone peculiar to the Mine, and are accompanied with fevcral Strata of different Matters, as Clay, Gravel, Rock, iSc. They who work in Mines, know by the Siz.e, and Colour of the Stones, when they approach the Vein. See Strata and Vein.

They difcover that there is a "Mine in a Mountain by the Marcafites, or Mineral Stones falling from it ; by the Mine- ral Tafle of the Waters ; by the Quality of the Exhalations rais'd from it; and by the difference between the Earth over the Mines % and that of the neighbouring parts in the cold time of Spring and Autumn, the Froft lying on the adjacent Places, when it thaws about the Mines. Add, that the Grounds producing but little Grafs, and that little, pale and colourlefs, is an indication of a Mine.

Some pretend to difcover Mines by the fole virtue of the Hazle-Tree, out of which they form a forked Stick, call'd Virgula diviuatoria, which, they fay, turns of itfelf, in their hands, but differently, according to the different nature of the Metals or Minerals underneath. This Artifice made a great noife in France towards the end of the 17 th Cen- tury 5 and the Corpttfcular Fhilofophy was call'd to account for it. But it is now in little Credit. See Virgula Di- vinatoria.

There ate fome Mines, wherein the Metals are found at their fir it openings very crude and imperfect ; which yet, in time, grow ripe and rich. Alonfo Hatha relates, that in Teicfi, Stones have frequently been thrown a fide, as not con- taining any thing coniiderable of Metal ; and yet have been tounJ many Years afterwards exceeding full thereof. Cxfalptms affurcs us, that Earths which yield no Metal at all, fometimes become very fertile Veins. In an Ifland of the 'Tyrrhene-Sea, after the Iron Mutes have been ex- haufted, they iiop 'em up abuut ten "Years, at the end whereof, they find 'em as rich as before.

For the Formation of Mineral and Metallic Matters in Mines, fee Mineral.

Mine, in the Art of War, is afubtcrraneous Canal, or Faffage dug under the Wall, or Rampart of a Fortification intended to be blown up by Gun-powder.

The Alky, or Paffage of a Mine, is ufually about four foot fquare 3 at the end of this is the Chamber of the Mme, which is a Cavity about five foot in width and in length, and about fix in height 5 and here the Gun-Powder is be- ftow'd.

The Sauc'idge of the Mine is the Train ; for which there is always a little Aperture left. See Savcidge.

There are various kinds of Mines, which acquire various Names; as Royal Mines, Serpentine Mines, Forked M-nes, according as their Pa&ages are ftrait, oblique, winding, &c.

There are alfo Mines made in the Field, which are call'd Foitgades. See Fougake.

Mines are either dug within the Body of the Earth, as thofe made by the Beheged to blow up the Works of the Befiegers, before they make a Lodgment on the Cover'd Way : Or in Eminences and Riling Grounds, as to make a Breach in the Ramparts, &c. Or to blow up Walls ; Or, laftly, to tear up Rocks.

M. Chevalier, in the Memoirs of the Royal Academy of Sciences, has handled the Subject of Mines with a great deal of Accuracy. He has calculated the Force of Gun- Powder, the Effort it makes, and the Refinance it meets with in heaving up the Ground. He fhews, that a Cubic Foot of Air inclufed in two Cubic Feet of Gun-Powder, is capable of lUftaining a Weight of near 290000 Pounds. But obferves withal, that this is vaftly greater than what it is found by Experience to have ; and that in fact, 340 Pounds of Powder don't raife above 30000 Pound of Earth. The Reafonof which difference he afcribesto feve- ral Caufes 3 as, that the Powder does not take fire all at once, fo that its force is divided; that part of the Shock is loft in the Canal or Paffage of the Mme, and in the Pores of the Bodies incom palling the Mine ; that the te- nacity of the parts of the Earth refill a feparation j that it is not enough that the Earth he fupported, but it mutt be carry'd upwards with a certain Velocity ; and that the Weight of the Atmofphere, is a very considerable ob- ftacle, ro which no regard is had in the Calculation. See

GuN-PoWDER*

From a great number of Experiments it appears, 1. That the EffecVofa Mme is always towards the weakeft fide; fo that the difpofition of the Chamber of a Mine does not at all contribute to determine this Effect: either one way or another, as the Miners miflakenly imagine. 2. That the Quantity of the Powder muft be greater or lefs, in proportion to the greater or lefs Weight of the Bodies to be rais'd, and to their greater or lefs Cohefion ; and the rcfult of all the Experiments that have been made for de- termining the different Quantity of Powder to be ufed for different Bodies, is to allow for each Cubic Fathom

c m )

MIN

Of Ioofe Earth, 9 or 10 Pounds of Powder.

Of firm folid Earth, and >

ttrongSand, 5 11 ot 1? -

Of Argil, or fat clayey Earth, r 5 or 16 Of new Mafonry, not very?

ftrongly bound, S'5 ori5

Of old Mafonry well bound, 25 or 30

3. That the Aperture, or Funnel of a Mine that has been play'dj if it had been rightly charg'd, is a Cone, the Diameter of whole Bafe is double the height taken from the Center of the Mme. 4. That when the Mine has been over-chaig'd, its Aperture is nearly Cylindrical, the upper Extremity not being much wider than the Chamber at bot- tom, where the Powder was lodg'd. 5. Thar, befide the /hock of the Powder again ft the Bodies it takes up, it likewife cruities all the Earth that borders upon it, both underneath and fide-ways, which Crufli extends itfelf the further as the Matters make the lefs Refiftance.

To account for all the Effects refuking from thefe Ex- periments, and to determine the Quantity of Powder re- quired for the charge of a Mine, and the mpft advanta- geous Difpofition for anfwering the Intent ; Let us con- ceive, 1. A Mine, whereof all the parts wherewith it is incompafled are incapable of being comprefs'd, and make an equable Refiftance, fuch as that of a Bomb equally thick throughout, fufpended in the Air* where it muft be ob- ferved, that befides the Refiftance of the Body, the Effort of the Powder muft likewife fuxmount the Weight of the ambient Air ; in which Cafe the Body will be beaten into Duff, or at leail into very fmall pieces.

a. Conceive a Mine incompafs'd wholly by fuch Bodies as are equally compreffible, and that refill every way with equal force. In this Cafe, the firft Effect: of the Powder will be to comprefs all thofe Bodies equally, and they will not be feparated, till by the Violence of their Compreffion, they are all incapable, any longer, to refiil its Effort; fo that unlefs the Powder be in a great Quantity, all its Effect: may end in the mere compreffion of the adjacent Bodies. For this reafon, they fometimes block up the Chamber of the Mme with large Beams, and fometimes wall it up with Stones, that the adjacent Bodies may refill the more.

Laftly, fuppofe a mme where all the Bodies that incom- pafs it, are equally compreffible, but where there is lefs Refiftance on one fide than another ; in this Cafe, there will be a Sphere of Compreffion, whofe Diameter will be fo much the greater, as the weak Side refills the more. With regard to which, there are three things to be confider'd,.

Firft, if the Effort of the Powder be very great with regard to the Refiftance of the weak Side, the Com- preffion will but reach a little way, that Side being tore off too fuddenly for the neighbouring parts to re- ceive their Shock. In which Cafe, the Aperture or Funnel will be almott Cylindrical, the Diameter of the upper Extreme not much exceeding that of the Chamber 3 and the Earth will be thrown to a great diflance, which the Enemy may make an advantage of, by making Lodgments in the Cavity, as was done at theSiegeof Verite; Secondly, If the Mme be under-charged, it only makes a fimple Compreffion on the weakeft Side, as it hapned at Cividad Rodrigo, Thirdly, If the Mine be charged with a Quan- tity of Powder between the two Extremes, it will raife a Cone of Earth, the Diameter of whofe Bafe will have a greater or lefs Ratio to its height from the Centre of the Mine, as the Effort of the Powder is greater or lefs. The moil advantageous Effect is when the Diameter of the Bafe of the Cone is double its height : In which cafe, the Earth blown up, falls almoft all back again into the Aperture of the Mine 5 fo that the Enemy cannot make any Lodg- ment.

To charge a Mine, therefore, foas it may have themoft advantageous Effect poffible, the Weight of the Matter to be carried up muft be known, ;'. e. the Solidity of a right Cone, whofe Bale is double the height of the Earth over the Centre of the Mme, which is eafily found from the Rules of Geometry, Having found the Solidity of the Cone in' cubic Fathoms, multiply the number of Fathoms by the number of Pounds of Powder neceffary for raifing the Matter it contains, according to the Proportion already laid down ; and if the Cone contains Matters of different Weights, take a mean Weight between 'em all j having always a regard to their degree of Cohefion.

As to the Difpofition of Mines, we have but one general Rule to lay down 5 which is, that the Side towards which. one would determine the Effect, be the weakeft. But this varies according to Occafions and Circumilances.

Knigh of the Mine, is a Military Honour, antiently con- fer'don Perfons who had diftinguifh'd themfelves in En- gagements mMines.

Mine Ships, are Ships fill M with Gun-Powder, indofed