heat will diffolve and raise up in fumes a great deal of the Terra Mercurialis Metallorum, which will occafion a poisonous Damp; and therefore it is neceffary that the gunpowder should be mixed with fomething that will prevent the folution, and fheath and envelope the acid particles of the falt petre and brimstone. Any unctuous or oily body will do it; and will be fo far from being detrimental to the blafting, that it will be rather of service to it, because it will add to the ftrength of the gunpowder, and make it do more execution than if it was used alone; and not only hinder its smoke from occafioning any noxious Damps, but deftroy the naturally poisonous qualities that lodge in the cavities of the Mine. The mixture that I would use with the gunpowder, is as follows:

Take one pound of gunpowder, one ounce of oil of turpentine, two drachms of camphor, and half a drachm of borax. Mix them well in a marble mortar, and they will be fit for immediate ufe.

Dr. Brown in his Travels and Obfervations on the Mines of Hungary, a book in which are many excellent remarks on Mines and Minerals, and highly useful to all concerned therein; says, that where an air Shaft cannot be conveniently funk, the Germans apply a large bellows with pipes of lead or leather to throw in air to the workmen. In the year 1696 this was put in practice, for the first time, in St. George's Adit in Goon-Laz in St. Agnes, where by reason of the great depth, (at least forty fathoms from grafs) it was impoffible to fink a Shaft, and to have fucceeded without this or fome other invention to convey air. It has been fince tried in other places with the like success, as I am informed, for I never faw it put in practice myself; indeed it was invented by the lord St. Albans, before the time of Brown's travels, and practised in Wales by his fervant Thomas Bufshet, Efq; (Fuller's Worthies in Wales, p. 4).

Now as we see fome Adits must have a great many Shafts to convey air to the workmen, as well as to fave the expence and trouble of rolling the broken work a great way back to the laft fhaft; fo it is neceffary likewife for them to understand the use of a dial compass, to direct them where to put down fuch Shafts as are wanted in their right places. Dialling is requifite in almost every Shaft they fink on an Adit, or elfe they may dig out of the way to no purpose; and when they work out of their right way in an Adit, it corrects and rectifies their miftake.

Indeed,

Indeed, without Dialling, they would often infenfibly go aftray from the line they had juft begun or proceeded in, and instead of working forwards towards the Mine, they may inadvertently drive in a contrary direction. It is true, a candle is a great guide to the labourers; for if they work fo ftraight as to fee a lighted candle that is placed where they began, they need fear no error, in case they began right; but if they once chance to work awry, and lose fight of the candle, it is no longer of any fervice for keeping them in a straight line.

This art of Dialling is also very useful, in directing them where to fink a Shaft exactly on any part or end in a Mine; and where to fink a Shaft for cutting the Lode, or Gunnies upon the underlie, which Shaft in fuch cafe is called an underlier. It is equally neceffary in other refpects for measuring the ground to the extent of this or that place or limit; for want of which knowledge, one set or party of adventurers may injure another, by encroaching on their property. Hence I apprehend, that Dialling, well and truly understood, is of no little confequence to the different neighbouring Lords and Bounders; otherwise it would be no difficult matter, for the adventurers to drive and dig promifcuously, into the feveral lands and properties of diftinct and separate perfons, whereby great confufion and lofs might enfue to fome or other of them; which this art effectually prevents, by ascertaining the just limits of each, and fixing their proper boundaries, through means of a line hung perpendicularly under-ground, with more exactness than is commonly fettled by hedges, ditches, ftones, or land-marks above-ground. Nothing can be more exact than a limitation of property, by the breadth of a fingle line; and yet I really believe a difference of one inch, in fome very rich Mines, might make a difference of several pounds to the different proprietors.

This laying out a traverse or measure under-ground, cannot, however, be very accurate with those, who take no account of the points or angles of the compass, but in lieu thereof, chalk the bearing of the line they measure with, on the board the compass lies in ; for if they are not exceedingly careful and precise in their operations, they may commit almost unpardonable and irretrievable blunders: yet formerly, before penmanship and figures were fo generally understood and practised among the common Tinners, as they are at prefent, most of our Mines and Adits were dialled for in this manner.

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The inftruments used for Dialling are, a compass without a gnomon or ftyle, but a center pin projecting from the middle of the compass to loop a line to, or stick a candle upon, fixed in a box exactly true and level with its furface, about fix, eight, or nine inches square, nicely glazed with ftrong white glass, and a cover suitable to it hung square and level with the upper part of the instrument: a twenty-four inch gauge or two feet rule, and a string or small cord with a plummet at the end of it: a little ftool, to place the dial horizontally : and pegs and pins of wood, a piece of chalk, and pen, ink, and paper.

The method of Dialling an Adit, in order to fink a new Shaft down-right upon its end, is this: firft they drop a line or plummet down in their last Shaft, in the middle of the breadth of the Adit; a man that ftands at the mouth of the Shaft aboveground, marks the place of the line there on a deal board flung across the Shaft, while the perfon who dials under-ground obferves the spot on which the plummet falls in the Adit; there he holds the end of a small cord in his hand, while another perfon carries the other part with him, as far as he can go in a ftraight line, without lofing fight of the Dialler's candle: the cord being drawn ftraight and tight, he holds it in the midst of the breadth of the Adit, while the Dialler fixes the fide of the compass accurately parallel with the line, and notes the bearing of the compass upon paper; and measuring the length of the cord to the other man's hand, he notes the length thereof on paper likewife. In the fame manner the Dialler takes his fecond measurement or draft, by setting his line and compass afresh, and proceeding as before, till he comes to the middle breadth of the Adit-end. This being done, he comes up from underground, obferves the place of the plummet line above at the Shaft, where he sets his compass, and lays off the very same traverse at grass which he took underneath; at the end of which, a new Shaft must be put down, directly on the Aditend. In case there are one, two, or many more angles or turns in the Adit, the compass must be reset at each of them, and their bearings or lengths measured, and taken down on paper; which will exactly answer to an experimental Dialler, by laying out the fame traverse above-ground, as hinted before.

Some, inftead of measuring each draft or length of cord, untwist it, and faften pins of wood numbered 1, 2, 3, and fo on, at the noted places, which may serve the purpose; but I

think

think it more regular to take the bearings of the compass on paper, and also the respective lengths, in columns oppofite each other. It is alfo to be remembered, that if the cord be wet in measuring under-ground, it ought to be the fame in measuring at grass, and vice verfa; otherwise it may cause no small error, because when wet it shrinks, and lengthens when dry.

To know the exact depth of an underlying Shaft, and a Winds, and how far a Gunnies may extend from the bottom of the Shaft to the brace of the Winds; you must order some one to defcend into the Shaft: then let your ftring down in the manner of a plumb, through a hole made in a deal board, laid across the brace of the windlass, taking the most convenient place where it will go deepeft, and not touch the fides of the Shaft. Where it touches at the bottom or underlying wall of the Shaft, there let a mark be made with a pick-axe. As the ftring hangs in the Shaft, apply the fide of your dial to it, as horizontally and directly across the Gunnies or excavated Lode (which is here in the Shaft, or the Shaft in the Lode, which you please) as you poffibly can, obferving what degree the needle stands on, which we will fuppofe to be fifty-two. This degree you must keep for your square. Then take up the string and measure it by the two feet rule, noting the length of the ftring on paper in rules and inches, under the word depth, as you are defired to obferve in the following example. You may fuppofe this depth to measure twenty-four rules, which you muft fet down, and the degree fifty-two directly against it.

Then go down to the bottom of the Shaft, where the mark was made. From hence you may begin to take the underlie of the Shaft, by laying a line horizontally across the Shaft from the mark, to the oppofite fide, roof, or hanging wall, of the Gunnies or excavated Lode; applying your dial to the fide of the line, or moving them up and down together, till you see the needle ftand upon your fquare degree fifty-two. Then drop your line and plummet from the roof or hanging wall of the Shaft, till they touch the fide or bottom wall, as you did before from the brace of the Shaft; and where the plummet touches at the bottom wall of the Shaft, make another mark. You must then measure the breadth of the Shaft from the bottom of the last plumb, to the oppofite or hanging wall, which we will suppose to be one rule twenty inches. Pull up the line, and measure its length from the rule to the mark below. This measure must be noted under the word depth; because, it is

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the fecond dropping or plumbing of the Shaft; and we will call it fixteen rules. This being noted under Depth, fifty-two under Degree, and one rule two inches under the word Length, as in the following example; you must descend to the place where the last mark was made, and lay the line horizontally across the Shaft from the mark to the oppofite fide or wall, applying your dial to the fide of the line, moving them up and down together, as you did before, till you fee the needle stand upon your degree fifty-two. The line and dial lying thus horizontally by the fide of each other, drop your line as far as it will go before the plummet touches the bottom wall of the Shaft, holding the line at the hanging wall where you will fee it will go deepeft, and not touch the fides. Here make another mark, where the plummet touches; which done, pull up your ftring, and measure this depth, measuring likewise the breadth of the Shaft where you held it: fuppofe you fay, depth twentyfix rules fourteen inches, degree fifty-two, and length or breadth two rules four inches. (See the example following). Here, the Shaft appears to be eight inches wider than it was, eight fathoms, five feet, and two inches higher up at the bottom of the last drop or plumb; a circumftance very common in all Shafts underlying with the Lode, as in fuch places the breadth of a Shaft muft depend upon the width of the Lode, if it is worth the breaking. But to proceed.

In order to make a third drop in the Shaft, before we arrive to the bottom of it (which I chufe to do, that it may appear in a more practical light, as fome Shafts underlie fo faft, as to require a great many drafts before the bottom can be dialled, and its pofition and depth afcertained) we will defcend to the mark laft made, where the Shaft is two rules four inches, or four feet four inches wide; and ftretch a line from the mark horizontally across the Shaft to the oppofite wall, applying the fide of the dial as before till the needle ftands on the degree fifty-two. The line must then be dropped till the plummet touches the bottom of the Shaft, clear from any contact with its fides. Here, at the plummet, a mark must be made alfo. Observing the breadth of the Shaft at the horizontal line, take up your plumb, and measure how many rules it is; fay twenty-eight rules twenty-two inches depth, fifty-two degrees; and the number of inches across the Shaft, fay one rule twelve inches, length, or breadth.

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