We shall obferve that this inflammable air, the condensed air N° 3, and the Pease Bloffom Damp, are never known in our Cornish Mines; but that the fixable air which is readily imitated by a mixture of oil of vitriol, water, and chalk, and extinguishes candles, is common to fome parts of them.

Dr. Conner in his Differt. Med. Phyf. relates a case of some people digging in a cellar at Paris, for fuppofed hidden treasure: after a few hours working, the maid going down to call her master, found them all in their digging poftures, but dead. The person who managed the fpade, and his attendant who fhovelled off the earth, were both on foot, and feemingly intent on their several offices: the wife of one of them, as if weary, was fitting on the fide of a hopper, and leaning her head on her arm; and a boy, with his breeches down, was evacuating on the edge of the pit, his eyes fixed on the ground: all of them, in fhort, in their natural poftures and actions, with open eyes, and mouths that seemed yet to breathe, but ftiff as ftatues, and cold as clay.

I have known fome inftances in Cornwall fimilar to this; and I prefume it has been often the cafe with us, that people have fallen into a pleafing kind of flumber, from which they never awoke: at least I have been told fo, by fome who had experienced the approaches of it upon themselves, and had the fortitude to shake off that fatal reverie, into which they had been infenfibly drawn. In the Mine of North-Downs, a drift end was in driving, where the air was fcarcely known to be fcanty one evening, at the ufual hour of relief, an elderly man, called Bamfield, and a boy, came to the Mine, and went down to their place, from whence the other workmen were juft come. Some time after the next hour of relief was elapfed, their partners were furprised that Bamfield and the boy did not come above ground. After waiting a little longer, they went down, and found the boy in a recumbent pofture; and Bamfield close to the end, fitting ftiff upon his breech, with both hands to his forehead, and his elbows refting on his knees, in a kind of fleepy nodding attitude; but both of them cold and stiff.

A want of air is indeed fo frequent, that few of our Shafts or Adits can be driven or funk to any confiderable depth or length, without fome degree of its ill effects; but as soon as they can conveniently give the Shaft or Adit a free communication of

air, they are relieved, and the Damp ceafes. For this purpose, they fometimes make ufe of a kind of air pipe, which conveys air down to the labourers: at other times, they fink a fide Shaft ; and as they go deeper in it, they work holes or drifts, as occafion ferves, from the fide Shaft into that which contains the Damp; and this communication between the two Shafts, gives the air a draft or current. But when this want of air happens at the end of an Adit, as it is very ufual, they use those methods of fallering, &c. already described, book iii. chap. 3. which fupplies them with air till a new Shaft is funk down upon the end, and holed to the Adit, which gives the men a free refpiration, and liberty of working, till another Shaft is requifite. Sometimes they are annoyed with Damps in dry fhallow pits, which are probably caused by noxious thick vapours that are emitted out of the pores of the earth; at other times, the Damps feem to proceed from the corrupt effluvia of ftagnating waters, that have lain a long time in the Lode or a Shaft. Both these Damps are so thick and heavy, that they kill and subdue the vivifying spirit of the air; so that for want of a fresh supply, the Miners cannot continue long under-ground.

Besides the finking of Shafts and putting down air pipes or the like, there are fome other things which help to fet the bad air in motion, and so serve in part to dispel the gross unwholefome vapours: thus, the drawing of water out of a Shaft, and the motion of the tackle, or the water that runs in an Adit, will help to diffipate the bad air; also, if faggots on fire or any burning fewel be thrown into a fuffocating Shaft, it will rarify the bad air for a while, and by the admiffion of fresh air the men may work fome time longer, till the Damp condenfes and gets to a head again.

Damps are generally moft common in fummer. About the dog-days we obferve they are not fo eafily remedied by air pipes and fallers, as in the other months; because the earth and atmosphere are greatly warmed by the folar rays, and the air itself is fo very calm and ferene, that for want of a due agitation thereof, Damps are occafionally more or less, from these circumstances of the season, and very often in those places which are not affected by them at other times of the year. When they blaft rocks by gunpowder they are frequently obliged to come above ground, and wait fome hours before they can venture down again, to work and clear away the fhattered ftones. Linden fays, he is fure, the smoke of the gunpowder with the

Fff

heat

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 fhould be mixed with fomething that will prevent the folution, and sheath and envelope the acid particles of the falt petre and brimstone. Any unctuous or oily body will do it; and will be so far from being detrimental to the blafting, that it will be rather of fervice to it, because it will add to the ftrength of the gunpowder, and make it do more execution than if it was ufed alone; and not only hinder its fmoke from occafioning any noxious Damps, but destroy the naturally poisonous qualities that lodge in the cavities of the Mine. The mixture that I would ufe 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 fuccefs, 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 practifed in Wales by his fervant Thomas Bufshet, Efq; (Fuller's Worthies in Wales, p. 4).

Now as we see some 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 last fhaft; fo it is neceffary likewife for them to understand the use of a dial compafs, to direct them where to put down fuch Shafts as are wanted in their right places. Dialling is requifite in almoft 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 mistake.

Indeed,

Indeed, without Dialling, they would often infenfibly go aftray from the line they had just 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 cafe they began right; but if they once chance to work awry, and lofe fight of the candle, it is no longer of any fervice for keeping them in a ftraight line.

This art of Dialling is alfo 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 fet 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 consequence to the different neighbouring Lords and Bounders; otherwise it would be no difficult matter, for the adventurers to drive and dig promifcuoufly, into the feveral lands and properties of diftinct and feparate 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 feveral pounds to the different proprietors.

This laying out a traverse or measure under-ground, cannot, however, be very accurate with thofe, 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, moft of our Mines and Adits were dialled for in this manner.

The

The inftruments ufed for Dialling are, a compass without a gnomon or ftyle, but a center pin projecting from the middle of the compafs to loop a line to, or flick a candle upon, fixed in a box exactly true and level with its furface, about fix, eight, or nine inches fquare, nicely glazed with ftrong white glafs, and a cover fuitable to it hung fquare and level with the upper part of the inftrument: a twenty-four inch gauge or two fect 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 laft 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 acrofs 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 compafs 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 likewife. In the fame manner the Dialler takes his fecond paper measurement or draft, by fetting 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 fets his compafs, and lays off the very fame traverse at grafs 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 meafuring 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 ferve the purpose; but I

think