OR Univerfal Dictionary OF KNOWLEDGE, COLLECTED FROM EVERY SOURCE; AND INTENDED TO SUPERSEDE THE USE OF ALL OTHER ENGLISH BOOKS OF REFERENCE. Illuftrated with Plates and Maps. IN TWENTY THREE VOLUMES. VOLUME XV. PERTH: PRINTED FOR C. MITCHEL AND CO. AND SOLD FOR THEM BY MR THOMAS OSTELL, AVE MARIA LANE, LONDON. AND ALL RESPECTABLE BOOKSELLERS. R. Morison, Printer. ENCYCLOPÆDIA PERTHENSİS. MIN M In your large heart was found a wealthy mine. Wailer. -A workman, to avoid idlenefs, worked in a For pit thereabouts, which was little Atem.d. Boyle-A mine-digger may meet with a xen, which he knows not what to make of. Boyles -The reedicis mine-man aims only at the obtain ma quantits of fuch a metal as may be vendible. 242. A cavern dag under any fortification but it may fok for want of fupport; or, in moteen, that powder may be lodged in it, which ged at a proper time, whatever is over it Aybe blown up and destroyed. What mine hath crit thrown down fo fair a tower? Sidney. - up the walls of Jerufalem, which you ae broken down, and fill up the mines that you Live digged. Whitgift. Others to a city ftrong Lay feze, encamp'd; by batt'ry, feale and mine, Alu ting. Milton. Mit, in the military art, ( I. def. 2.) Se. Mivo y II. in laft volume, P. 720. From «ght number of experiments, it appears, 1. That the force of a mine is always towards the weket de; fo that the difpolition of the chamAero. a mine does not at all contribute to deterThe this effect. 2. That the quantity of powdrmut be greater or lefs in proportion to the tre or le's weight of the bodies to be raifed, d to their greater or lefs cohefion; fo that we allow for each cubic fathom, of loofe earth, 9 or tol. Of firm earth and strong fand, 11 or b. Of fat clayey earth, 15 or 13 lb. Of new malory, not ftrongly bound, 15 or 20 lb.; and of old mafonry, weil bound, 25 or 30 lb. 3. That the aperture, or entonnoir of a mine, if rightI charged, is a cone, the diameter of whofe VOL. XV. PART I. MIN bafe is double the height taken from the centre. of the mine. 4. That when the mine has been overcharged, its entonmoir is nearly cylindrical, the diameter of the upper extreme not much exceeding that of the chamber. 5. That befides the fhock of the powder against the bodies it takes up,. it likewife crushes all the earth that borders upon it, both underneath and fidewife. To charge a mine fo as to have the most advantageous effect, the weight of the matter to be carried must be known; that is, the folidity of a right cene, whofe bafe is double the height of the earth over the centre of the mine: thus, having found the folidity of the cone in cubic fathoms, multiply the number of fathoms by the number of pounds of powder ne celery for raifing the matter it contains; and if the cone contains matters of different weights, take a mean weight between them all, always haz ving a regard to their degree of cohefion. As to the difpofition of mines, there is but one general rule, viz. that the fide towards which one would deter mine the effect be the weakeft; but this varies, according to circumstances. The calculation of mines is generally built upon this hypothesis, That the entonhoir of a mine is the fruftum of an inverted cone, whofe altitude is equal to the radius of the excavation of the mine, and the diameter of the whole leffer bafe is equal to the line of leaft refiftance; and though thefe fuppofitions are not quite exact, yet the calculations of mines deduced from them have proved fuccef fal in practice; for which reafon this calculation thould be followed till a better and more fimple one be found out. M. De Valliere found that the entonnoir of a mine was a parabaloid, which is a folid generated by the rotation of a femiparabola about its axis; but as the difference between thefe two is very infignificant in practice, that of the fruftum of a cone may be used. (III. 1.) MINE in natural hiftory, (§ II. def. 1.) implies a deep pit under ground, whence various kinds of minerals are dug out; but is more parti A cularly |
