the needle being rectified to the degree fifty-two, make a mark at one rule twenty inches upon the ground; and thus you have done the first degree. In like manner you may do all the reft, if you go over these degrees fingly, one by one; but as here are feveral fquare degrees (fifty-two) before you come to any bye one, which goes upon the courfe of the Lode, you may take all thefe fquare degrees together, firft adding their lengths together, to know how many inches and rules they are.

The lengths oppofite the fecond, third, fourth, and fifth dergees (fifty-two) are equal to three rules forty-fix inches, which by reduction amount to two fathoms, one foot, ten inches, the exact underlie of your Shaft; therefore if you first measure out fo much of your ftring or line, and the needle is rectified to fifty-two, bid your afliftant make a mark there: thus you take all the four degrees together and find the mark at grafs, which he made at the bottom of the Shaft.

Go to the

your next

mark your affiftant made, and look to your notes for length, measuring out fo much upon your cord, viz. twentytwo rules eight inches; then let him go forward with one end, and caufe fome one to hold the other end in the mark he made laft: look to your notes for your degree over against that length, which is thirty-fix, and rectify your needle to it; let him that has the plummet end of the line, bring the ftring to the fide of the Dial, yourself standing at fome diftance from him that holds the other end in the mark. The ftring lying exactly even with the fide of the Dial, and the needle ftanding upon the bye degree thirty-fix, bid him make a mark at the end of the plummet, and fo you have done that length.

your

your

Now to go laft mark, and put one end of rule to it, and fet the needle upon fifty-two, laying the edge of the rule parallel to the fide of the Dial. This length being but ten inches, make a mark there.

Look into your notes for your next length, which is twentyfour rules fourteen inches: measure this out, and let your affiftant go on with the ftring, caufing the other end to be held in the laft mark. Set the needle upon thirty-fix, the degree oppofite that length; apply the line exactly parallel to the fide of the Dial and stretch it tight. At the plummet end of the ftring make a mark, which finishes another length. Lastly, because the other two lengths are both to be taken upon one degree, and there being no other bye degree between them,

you

you may add the lengths together, and take them at once, which are two rules and eight inches, the needle standing upon the degree fifty-two. The end hereof is the place at grafs, directly over the mark you made at the bottom of the Winds. Here, if there is a neceflity for it, or it is worth your trouble and expence, you may fink a new Shaft down-right upon the bottom of the Winds, which you may as infallibly depend upon performing, as on any the most facile transaction in Mining. No one thing is more commonly done; it being often of the laft importance to fink down a new Shaft, and thereby fave the charge of drawing the work by a double draft. It is not always requifite to fink a new Shaft, directly on the Winds; but whenever it is thought fo, the undertakers muft firft dial underground and afterwards at grafs, before they can presume to fink a perpendicular Shaft upon the Winds bottom.

Now, to know whether you have dialled this exactly or not, without going over it again, add all your square short lengths oppofite the degree fifty-two together: the fum will be nine rules, fixteen inches; which, by reduction, make three fathoms, one foot, four inches, the exact declination or underlie of your Lode in the Shaft and Winds, from the brace of the former to the bottom of the latter at fifty-one fathoms, one foot, eight inches, the depth of the Mine or Lode in that place. Again, if you chufe to afcertain the average underlie of the Lode, for one fathom with the other, you must work the above drafts by the rule of three direct; by which it will appear, that for that for every fathom the Lode has been wrought in perpendicular depth, its inclination or underlie is four inches and a half. This underlie is very small and fcarcely merits the name in Cornwall, where frequently our Lodes underlie a fathom in a fathom, and feldom lefs than two feet in a fathom. Indeed, fome few Lodes go down in form of a Zig-Zag; and by that means, at a great depth, deviate from a perpendicular very little from the place where they first begin to fink: but this is very rare; and though it may fave coft in not finking many underliers and winds, yet the conveniency is over ballanced by having a lefs quantity of Mineral in a given perpendicular Lode, than in that which underlies one half in the other. That is, a Lode that underlies three feet to the right or left from a perpendicular, will measure nine feet in depth for every fix of a central tendency.

But to proceed you must next add

in laying out the drafts upon the surface. the lengths you took upon the course or

up

run

run of the Lode, which were but two; viz. twenty-two rules, eight inches, and twenty-four rules, fourteen inches, in all, forty-fix rules and twenty-two inches; which, by reduction, are equal to fifteen fathoms, three feet, ten inches: measure thefe out with your rule and line, and give your plummet to the affiftant, to go on with the fuppofed run of the Lode, caufing fome one to hold the other end at the board upon the Shaft brace, where you firft began to plumb: then go to the middle of the ftring, and fetting the needle upon the degree thirty-fix, apply the line exactly parallel to the fide of the Dial, and bid the affiftant make a mark at the end: go to this end or mark, and measure out your fquare lengths, which in all are three fathoms, one foot, four inches: then give your aslistant the end, holding the other end in the mark; fet the needle upon fifty-two, and bid him apply the line exactly parallel with the box, and make his mark. If this mark hit that you made, when you dialled it before, you have done the work exactly; otherwife, you have committed fome blunder, and ought to try it over again for this rule always holds true when you take fquare lengths, and your lengths forward, on the courfe of the Lode or any way, by one degree; as you here took thirty-fix for your degree.

Many more examples in Dialling might be given, fuch as, to dial Shafts and Winds that underlie and beat into the end; to dial in a Gunnies with many crofs drifts and turnings, and afterwards to fquare the fame at grafs, &c.: but as they are already given in Houghton's Rara Avis, and Hardy's Miner's Guide, and as one hour's conversation with practical Miners will illustrate the fubject better than a week's reading, I shall conclude what I have faid on it, with this fingle remark, that the crude, goffany, ferruginous Ores in the Mines, have no influence on the needle of the compass: I have often found, that even the magnet or loadstone will not attract pure Iron Ore (much less the ferruginous Ores of other Metals) till they have undergone the fire, by a calcining heat, or fome other process ; otherwise, there could be no poffibility of Dialling most Copper Mines, because they commonly abound with much Iron (Goffan) in Copper Ores.

The other branch of Dialling, is properly ftiled Levelling; which is an operation to find the inequality, afcent, and defcent, of any ground or hill. Hence it is of great use for all aqueducts to towns, houses, ponds, mills, &c. and particularly in Mining,

either

either to bring a water course to a Mine, in order to erect an engine, or elfe to find how deep an intended adit will be from or to a prefixed or given place. But as the rules of this art are fully laid down in books that treat on land furveying, I need not dwell on it here; efpecially as the two authors above mentioned have defcribed its use and application to our fubject. Neither is it neceffary to defcribe the feveral inftruments and improvements that have from time to time been made and used in Levelling, fince the Miners, inftead of the true Levelling inftruments, called the air level, or fpirit level, commonly fubstitute (though not to their credit, for the best may be had at little expence) a water level of their own construction; which is generally a clumfy inftrument in form of a small narrow trough, an inch wide, and three feet long, planed very exact and truc.

To find the fall or declination of the ground, they lay this Levelling inftrument on the highest part of the ground they are about to level or meafure, and by pouring water into the trough, they eafily perceive when it lies truly horizontal, and then they proceed in the fame manner that is practifed by others who ufe the air level. But when a Mine lies on a steep hill, and there is room for a proper station below for taking a juft obfervation by a quadrant of altitude, then the height of the hill (which is the fame as the level or depth of the adit at the Mine) may be eafily found by the rules of altimetry. The theory of thefe operations, however, is not confidered by the Miners; neither is a fmall error difcoverable, because they feldom level any great length of ground at one time, and content themselves with the common manual operations.

Dr. Halley fuggested a new way of Levelling which is wholly performed by the barometer, in which the mercury is found to be fufpended to fo much the less height, as the place is further remote from the center of the earth. Hence it follows, that the different height of the mercury in two places gives the difference of level. Mr. Derham found, from fome obfervations at the top and bottom of the monument in London, that the mercury fell one-tenth of an inch at every eighty-two feet of perpendicular afcent, when the mercury was at thirty inches. Dr. Halley allows of one-tenth of an inch for every thirty yards; and confidering how accurately barometers are now made, he thinks they are fufficiently exact to take Levels for the conveyance of water, and less liable to errors than the common Levels.

Some years fince, the reverend Mr. John Pickering, Mr. R. Phillips, Mr. Waltire a travelling lecturer on philofophy, and myfelf, took the altitude of the highest eminence of the celebrated Druids hill called Carn Brea, by one of Mr. Waltire's best barometers; when we made the utmost perpendicular height, at the luftration rock bafons, three hundred and fixty feet or fixty fathoms from the bottom of Redruth town. Nevertheless, one great obftacle to this way of menfuration in our county, arifes from the fudden and frequent changes of our atmosphere, which muft influence the mercury, and cause some difference between the spot of departure, and the place of deftination, in proportion as the atmosphere alters; fo that this method can be ufed only in clear, ferene, and fettled weather.

BOOK