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 first began to plumb: then go to the middle of the ftring, and setting 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 affiftant the end, holding the other end in the mark; set 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; otherwise, 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-six for your degree.

Many more examples in Dialling might be given, such as, to dial Shafts and Winds that underlie and beat into the end ; to dial in a Gunnies with many cross 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 illuftrate the fubject better than a week's reading, I fhall 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 some other process; otherwise, there could be no poffibility of Dialling moft 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 descent, of any ground or hill. Hence it is of great ufe 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 else 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; especially 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 instruments, called the air level, or fpirit level, commonly fubftitute (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 clumsy instrument in form of a small narrow trough, an inch wide, and three feet long, planed very exact and true.

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 measure, 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 use the air level. But when a Mine lies on a steep hill, and there is room for a proper station below for taking a just observation 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 easily found by the rules of altimetry. The theory of these operations, however, is not confidered by the Miners; neither is a fmall error discoverable, because they feldom level any great length of ground at one time, and content themselves with the common manual operations.

Dr. Halley suggested a new way of Levelling which is wholly performed by the barometer, in which the mercury is found to be suspended to so 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 observations 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 philosophy, and myself, 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 basons, 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 sudden and frequent changes of our atmosphere, which must influence the mercury, and cause some difference between the fpot of departure, and the place of destination, in proportion as the atmosphere alters; so that this method can be used only in clear, ferene, and fettled weather.

BOOK

BOOK IV.

CHA P. I.

The Method of Sampling and Vanning of Tin-stuff, with the Stamping, Burning or Calcining, and Dreffing the fame ; with the Manner of Dreffing the Leavings, Loobs, &c.

T

IN-STUFF that lies by the fide of the Shaft, when it becomes a great heap, or if it otherwise suits the humour of the concerned, is firft spalled or broken to the fize of a man's fift or lefs, by which the most indifferent parts are separated and forted from the best; so that perhaps not more than one half of a large heap may be referved for dividing and stamping. After the Tin-ftuff is thus culled, and properly fized, it is divided out in smaller heaps by measure of a handbarrow, that usually contains a fack and a half, or eighteen gallons. These shares, which they term Doles, are parcelled out into fo many different heaps on any the moft adjacent parts of the field, fometimes to the great prejudice of the husbandman, who is not confidered for his damage by the lord of the foil, or the owners of the Mine. The method and number of Doles, into which Tin-ftuff is frequently divided, may be seen in book. iii. chap. iv. The parcels being laid forth, lots are caft; and then every parcel has a distinct mark laid on it, with one, two, or three ftones; and sometimes a bit of stick with the initials of the proprietor's name, or a turf laid on the middle of the Dole. When thefe marks are fixed, the Doles may continue there unmolefted for any length of time: the property is fettled; and no one, but the right owner, may add or take from it.

The Doles which are defigned for fale, are very accurately measured; for as the barrows are carried off for their respective divifions, one perfon, who is the reckoner, keeps an account by making a notch in a stick for every barrow; and if there be an odd one left, it is equally divided by the gallon, the shovel, and, when it is rich, even by the handful. The Doles being divided, they proceed to caft lots for that which fhall be

fampled.

fampled. This Dole being turned over, equally levelled and mixed, is then divided by a man with his fhovel, into two equal parts, taking a little of the Tin-stuff from one end to the other of each of thofe parts to the amount of fome gallons if the Dole is pretty large. This quantum is bruised down by large fledges to the fize of an hazle nut, then equally levelled and divided into four parts, two oppofite quarters of which are selected and bruised over again to a smaller fize. These reductions and smaller divifions are repeated again and again ad libitum; till the quantity defigned for fampling, is well mixed, and made as fine as common fand; when each sampler fills his little canvas bag with it, and proceeds to a trial of its value by water, in the following manner.

To make a rough guess or coarse effay, the sampler takes a handful of it, and washes it on a fhovel, till the impure earthy parts are carried off by the water from its fides. The more ftony, folid, heavy particles being left behind, they are bruised by an affiftant, with a fledge on the fhovel, till the whole affumes the appearance of mud. This is washed again, till it lofes its muddy afpect; when by a peculiar motion of the shovel not to be described, the metallick particles are collected together on the fore part or point of it. By repeating these bruifings, washings, and motions, it becomes clean black Tin, fit for the fmelting furnace. This is called a Van (from the French word Avant, foremost, as I apprehend) it being thrown forth upon the point of the fhovel, by the dexterity of the fample-trier. After the Tin is thus made clean to his mind, he dries it; and if it be as much black Tin as will entirely cover a good fhilling, or rather if it is the weight of a fhilling, he terms it a Shilling Van, which is not rich; but if the Van will cover or equal the weight of a crown piece, it is good Tin-stuff, and is termed a Crown Van. Now they fay, the Shilling Van will produce one hundred grofs or avordupois weight of block or white Tin; and the Crown Van will yield five hundred weight of block Tin, for every hundred facks in measure, of the respective Doles that the fample or Van is taken from, and fo proportionally on, to the richeft Tin-ftuff called Scove, which is reckoned ten thoufand of white Tin-metal every hundred facks; or in other words, it will produce one hundred hundred weight of Tinmetal, for each hundred facks of Tin-ftuff; yet there is none near so rich as this in any quantity, except a particular stone or lump.

But