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OR
OF

KNOWLEDGE,

COLLECTED FROM EVERT SOURCEs

AND INTENDED TO

SUPERSEDE THE USE OF ALL OTHER ENGLISH BOOtfS OF REFERENCE.

JfluftrateD ttritf) plates anD 9@ap#.

IN TWENTY THREE VOLUMES.
VOLUME XV.
PERTH:

PRINTED FOR C. MITCHEL AND CO.
ASD SOLD FOR THEM BY MR THOMAS OSTELL, AVE MARIA LANE, LONDON.
SOLO ALSO BY MESS. YERNOR, HOOD, AND SHARPE, LONDON;
AND ALL RESPECTABLE BOOKSELLERS.

A. Morison, Printer.

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ENCYCLOPÆDIA PERTHENSIS,

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M I N

height taken from the centre. That when the mine has been overcharged, its entonm>ir is nearly cylindrical* the diameter of the upper extreme not much exceeding that of the chamber, r. That besides the shock of the powder against the bodies it takes up, it likewise crushes ait the earth that borders upon it, both underneath and sidewise. To charge a mine so as to have the most advantageous effects the weight of the matter to be carried mull be known; that is, the solidity os a right cfnjt, whose base is. double the height of the eaith offer the centre of the mine: thus, having round the solidity of the, co"e in cubic fathoms, multiply the number of

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fathoms by the number of pounds ot powder ne-i celliry for raising the matter it contains; and if the cone contains matters of different weights, taHe a mean weight between them ail, always haJ SUnex. ving a regard to their degree of cohefioD. As to the up the walls of Jerusalem, which you /disposition of mines, there is but one general rule,

■ '' •• -u:ch one would deter-' est > but this varies according to circumstances. Tiie calculation ot mines is generally built upon this hypo.thtsu, That the entonhoirof a mine is the frustum of an inverted cone, whose altitude is equal to the radius of the excavation of ths mine, and the diameter of the whole lesser base is equal to the line of lealt resistance'; and though these suppositions art not quite exact, yet the calculations of mines deduced from them have proved lncccs.su! in!

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~*cbrjkcTi down, and siW up the minei that you' viz', that the side towards whii
^•t >%cd. ffbagi/t.— mine the eiTect be the weak

Others to a city strong
la* fc?c, encimp'd; by balt'ry, scale and mine,
.VTiu.tiiig. Milton.
■.II.1 Mut, irl tfce military art, I. def. x.)
»«£)IL in last volume, p. jio. From
* pt<i number of experiments, it appears, I,.
Tf^tthe force of 2 mine is always towards the
T<lici iic; so that the disposition of the chani-
I'.to. i mine does not at all contribute to deter-

"iie this cfect. *.T.lat the quiutilyof po.v- practice; for which reason this calculation mould mist be greater or less in proportion to the be followed till a better and more simple one ^•Jtayr less weight of the bodies to be raised, be found out. M. Dc Valhere found that the -altJtieir greater or kss cohesion; so that we er.tonnoir of a mine was a p.irabaloid, which is a fallow for each cubic fathom, of loose earth, solid generated by the rotation t>f a semiparabola 1"idH. Of tirm earth and strong sand, II or about its axis; but as the difference between ;i '*>• Ot Bit chyey earth, 15 or 1S lb. Of new these two is Very insignificant in practice, that of

the frustum of a cone may be used.

(III. 1.) Mine in natural history, II. its. 1.) implies a deep pit tinder ground, whence various kinds of minerals are dug out; but is more partiA - cularljr

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