consider as being 130 long. By means of a scale take the point D, making CD equal to 10, orth of CN. Draw DA parallel to CW, cutting the circumference at the point A. Join CA, and the line CA will represent the direction of one of the levels, for the point A will be 1 above C, and CA is 130 long. Place one leg of the compasses on W, and extend the other to A, and then measure that distance on the same scale of chords used before, and it will read about 410; or the lines CW and CA may be continued on the paper a suitable length in a direction from C and the protractor placed on the paper with its centre at C and the angle ACW may be thus read off, and it will be found to be about 4°. The bearing of the level CA then is 90 4 = 851° N.W. approximately, because it cannot be read to exact minutes this way. In the same manner a level course going on the opposite side from C may be shown to have a bearing of N. 85° E.

--

If a protractor is not allowed, or is not at hand, a very close approximation to a correct answer may be obtained without it, thus :

From the centre C, Fig. 752, with the radius 130, describe the circle NESW. Let NS represent the north and south, and E and W the east and west points respectively on the circle. Make CD equal to 10, and draw DA parallel to CW, cutting the circumference at the point A. Join CA and WN. Then CA will represent the direction of the level course and A will be 1 above C or W.

Bisect the chord WN in F and join CF. Continue the line CF to cut the circumference in G. Then the length of the chord WN is 1302 + 1302 = 183.847, and since the point N is 13 above C, the point F is 6.5 above C. The angle CWF is equal to the angle WCF, therefore the side CF is equal to the side WF, 183.847 and WF is. =91924. As F is 6'5 above C, it will be found that the

2

point G is as 91924: 130 :: 65: 9'1924.

99'17

=

2

49'585.

Now join GW, and its length will be 919242 + (130 — 91*924)2 = V919242 = 99'17. Bisect WG in H and WH = 91924 +380769917. Join CH, and continue CH to cut the circumference in J. 6:1924 = 4'5962 above C or W. Find the versed sine JH in

2

The point H is

the segment GW

49'5852 =

by the formula given in Answer 149, thus 130 √130 9828. Therefore CH = 130 – 9.828 = 120 172. As H is 4'5962 above C, the point J is as 120 172: 130:: 4'5962: 4'972. The angle GCW contains 45° and JCW 2210, and approximately the proportion of degrees for the angle ACW will be found, thus as 4'972:1:22:4525, or, say, 4, and therefore the bearing of the level CA is approximately 90° - 44 85 N.W. The level proceeding on the opposite side will bear approximately N. 851 E.

=

10

10

10

The most satisfactory, and indeed the only strictly accurate, answer to a question of this sort is obtained from a solution by trigonometrical rules, involving the use of tables, &c.

CHAPTER XV.

LIGHTING: SAFETY-LAMPS: FIREDAMP DETECTORS: CARBONIC ACID GAS DETECTOR: NAKED LIGHTS.

Early Lighting-The Steel Mill-Humboldt's Lamp-The Davy Lamp-The Stephenson-The Clanny-Morgan's-Protector-Gray's-Hepplewhite-Gray - Marsaut - Mueseler-Ashworth's Mueseler-Evan Thomas-Clifford-McKinless-Howat Deflector-ThorneburryMarshall's-Porch Lamp-Purdy's Lock-Craig & Bidder's Magnetic Lock-Cuvelier's Patent Lock-Extinguishing Locks-Lead Rivets-Wolstenholme Locking Machine-Lead Rivet Moulding Machine--Lighting and Re-Lighting Locked Lamps-Shields-Shut-OffsWick-Illuminants-Glasses-Cleaning Lamps-Lamp Room-Examining and Testing Safety-lamps before going into the Mine-Patterson's Testing Apparatus-Photometric Tests-Use of Lamps-Primary and Secondary Portable Electric Safety-lamps-Ansell's Diffusion Detector-Forbes' Damposcope-Hardy Detector-Aitken Indicator-Angus Smith's Air Compression Syringe-Liveing's Firedamp Detector-Maurice's Firedamp Indicator-Coquillon's Indicator-Le Châtelier's Eudiometer-The Shaw Gas-Tester-Garforth's Ball Detector-Safety Lamp Alarm Arrangements-Mallard & Le Châtelier's Safety LampPieler Lamp--Ashworth's Benzoline Lamp-Chesneau Lamp-Stokes' Alcohol Flame Testing Lamp Hydrogen Gas Testing Lamp-The Test Chamber for Observing Flame CapsCarbonic Acid Gas Detector-Candles and Small Oil Lamps-Large Oil Lamps--Sinclair's Comet Lamp.

EARLY LIGHTING.

In the early days of mining in this country torches are believed to have been used for lighting the outcrop workings. In the event of firedamp being found in troublesome quantities the simple workings were readily abandoned and fresh ones sought. The danger of explosion, however, was not so great as might be supposed, owing to the fact that marsh gas requires a certain proportion of atmosphere to be mixed with it in order to become explosive, or capable of ignition, whereas in primitive mines there was little, if any, circulation of air in the workings. Explosive mixtures, therefore, seldom existed, and even when an explosion occurred its effects must have been confined within comparatively narrow limits.

In other countries, on the Continent, relics in ancient mines give ground for the belief that earthen oil lamps, similar in shape to those now made, were used instead of torches. In later days the fear of danger in fiery mines led to the use of dried fish skins from the scales of which a faint phosphorescence was given. Such methods, however, must have been very inadequate, and in point of fact mining operations were often carried on without any light. The difficulties and dangers of working under such circumstances must have been very great, and although the danger of exploding the firedamp was thus obviated, yet the means of detecting noxious gases and other perils were equally absent. When serious difficulties were encountered which baffled the skill and courage or the appliances of the miner, he would readily desert the shallow shafts or adits in which the coal seams were inexpensively won, and would pursue his experiments elsewhere. Tallow candles were used in the workings and in searching for gas. A search for gas consisted in "trying the candle." A small candle (30 or 40 to the lb.) was carried in a lump of wet clay, and the flame reduced in size by placing clay at its lower extremity near the exposed portion of wick. The candle was raised

from the floor very gradually in an upright position with one hand of the observer held palm outwards towards the light to shield it entirely from view except the very tip of the flame. As it was raised an appearance of "top" or cap" of blue flame above the candle flame indicated the presence of gas in the air. As soon as this appeared the candle would be quietly lowered, the searcher would withdraw with as little disturbance as possible, and some means would then be resorted to for dispersing the gaseous mixture. Where the quantity of gas was small attempts were sometimes made to get rid of it by beating it out with a coat or with a piece of brattice cloth. Before commencing to do this the man would retire to a distance, choosing a position away from the out-going current. His candle would be left here in a refuge of safety out of reach of the passing fire-damp. Another plan of disposing of gas believed to be present only in small quantity was to set fire to it. This was done at night after the withdrawal of the colliers from the working faces by a special operator with a good nerve, and sometimes a suitable dress. The dress was of wool or leather well damped, the face and head being further protected by a mask and a hood. Provided with a long stick, to the end of which his

lighted candle was attached, he would crawl for the last few yards before reaching the explosive mixture previously discovered, and at the moment of firing it, would keep his candle the length of the stick in front of him, taking care to keep his body and head down on the floor that air might reach him during the passage of the explosion flame. When this had passed, in order that he might avoid the carbonic acid gas left by the explosion, he would immediately stand upright, or as nearly upright as the height of the road allowed. This officer of the colliery was called a "fireman" in this country, a name which is still retained to the present day for the man who searches for gas. In some countries he was called the penitent, on account of the resemblance of his dress to that of certain religious orders in the Roman Catholic Church. In many instances, in spite of all precautions, the fireman fell a victim to the explosion he thus caused.

The Steel Mill.-Frequent explosions of fire-damp rendered it highly desirable that a light should be introduced into mines which would be incapable of firing the surrounding atmosphere, and about the year 1760 the "Steel Mill" was invented by Spedding of Whitehaven, its object being to produce a shower of sparks which would give sufficient light to the collier, and yet would not fire an explosive mixture of gas and air.

Fig. 753 shows the Steel Mill while in use throwing upwards a stream of sparks made by a sharp piece of flint in contact with the steel rim of a rapidly revolving wheel. A brass wheel about 5 inches in diameter having 52 teeth, works a pinion having 11 teeth, the latter being on the same axle as the thin steel-rimmed wheel against which the flint is pressed.

For this illustration we are indebted to the "Proceedings of the South Wales Institute of Mining Engineers," Vol. XVII., p. 125.

The three wheels are carried in a light iron frame, as shown in the illustration. and the whole, when in use, was supported by means of a detachable leather band passing through the back end of the frame and round the neck of the operator, who turned the handle attached to the axle of the driving wheel. Both hands were thus at liberty for use in working the mill, which required all the energies of a strong boy.

Frequently several steel mills had to be set going or "played," as it was called, in one place at the same time in order to get sufficient light, and it has been stated that at an ordinary North of England colliery their cost amounted to £80 per fortnight. This cost would be for the wages of those working them.

The sparks from a steel mill have a bright appearance in a pure atmosphere, but when discharged into explosive mixtures of gas and air their size and luminosity are increased according to the explosive proportions, and when the mixture of air and gas is in its most violently explosive state, if not before, these sparks are quite capable of themselves causing an explosion. The presence of carbonic acid gas or a preponderance of marsh gas beyond the explosive point is said to have been indicated by the sparks assuming a bloodred colour.

Notwithstanding the feeble glimmer of light obtained at great cost from the steel mill, and the fact that it caused explosions, it remained in use at any rate down to the introduction of safety-lamps in 1815. Whatever faith existed up to 1785 that the steel mill would not cause an explosion of fire-damp was then rudely shattered, as may be gathered from the following entry in Sykes' Local Records of Northumberland and Durham, &c. :—

"1785 (June).—An explosion occurred in Wallsend Colliery, by which one man lost his life. This was the first explosion which was distinctly known to have taken place at the steel mill. Some doubt remained up to this time as to whether the fire-damp would explode at the spark of the steel mill or not; but the fact was clearly ascertained on this occasion, as the person, John Selkirk, who was playing' the mill at the time, survived the accident."

About this time Wallsend was the deepest colliery on the Tyne, being stated by Brand in 1787 to be 105 fathoms deep.

The same Local Records tell us that this explosion had been closely preceded by two others at the same colliery, one in November, 1784, by which three men lost their lives, and the other in December, 1784, resulting in two deaths. "These explosions were supposed to have taken place at the spark of the steel mill, by the light of which the people were working in the shaft. The bodies were not recovered for several months."

The remaining part of the entry for November and December, 1784, is interesting, as showing the date at which attempts were first made to use reflected sunlight in the shafts:-"In repairing the shaft after these explosions, the mode of throwing the rays of the sun down a shaft by a mirror, so as to light it, was accidentally discovered in the following manner :-While the people were working in the shaft, at about 80 fathoms from the surface, a carpenter was employed to do something at the head framing, immediately above the mouth of the shaft. and in using his saw, he turned the bright blade of it, accidentally, so as to throw a pencil of the sun's rays suddenly down the pit, to the great terror of the workmen below, who thought the pit had fired again. The cause of their alarm being, however, soon discovered, it suggested the idea of applying a mirror to throw the light of the sun down the shaft, which mode of lighting has since been frequently resorted to when other lights could not be used."

The light obtained from the reflection of the sun's rays must have been quite inadequate for workings, however limited in extent, for even on bright days such

reflected rays could not have penetrated far from the shaft owing to obstructions in the galleries, while on sunless days not the faintest glimmer of light could have relieved the absolute darkness of the mine.

SAFETY LAMPS.

Humboldt's Lamp.-An ingenious lamp was designed by Humboldt in 1796, which burned without drawing the feed air from a surrounding atmosphere. It was only used for experimental purposes, as it very soon went out.

Clanny's First Lamp.-In 1813 a society for the prevention of accidents in coal mines was formed in Sunderland, and in the same year Dr. William Reid Clanny, of that town, devised and exhibited at the meetings of the society a lamp which was afterwards tried in an inflammable mixture of air and gas at the Herrington Mill pit, in the county of Durham, on October 16, and again on November 20, 1815. The flame of this lamp was insulated, and the air supply necessary for its combustion was blown through a stratum of water placed below by means of a pair of bellows. A second layer of water was arranged above the flame through which the products of combustion escaped. The water thus separated the air around the flame from that outside the lamp. In an explosive atmosphere it went out. This lamp was too unwieldy to be useful, and after being used experimentally was quickly superseded by later inventions.

The Davy Lamp.-In August, 1815, Sir Humphry Davy visited the collieries near Newcastle-upon-Tyne to investigate the nature of mine gases, and on November 9 of the same year read his celebrated paper on fire-damp before the Royal Society of London. This paper was published in the Philosophical Transactions of that Society, and contains a fascinating account of the experiments undertaken by Davy, which led to his safety-lamp, especially interesting in view of later inventions in the same line.

A flame is always a burning gas, whether supplied directly as in the case of ordinary coal gas, or made from a liquid as in the case of oil lamps, or from solids as in the case of candles, or produced from the burning of wood or coal. In all cases the material, whether yielding one gas or more, takes a gaseous form before the appearance of flame. Before a gas can burn it must be first heated to what is called its temperature of ignition.

Davy found that fire-damp requires an admixture of a large quantity of atmospheric air to render it explosive. He experimented with small metallic tubes and sieves of brass and iron wire gauze, which he found, under certain conditions, prevented the passage of flame. Small metal rings have a remarkable power of reducing the size and illuminating power of the flame. Smaller rings were tried and altogether prevented the passage of flame. Metallic tubes one-fifth of an inch in diameter and 1 inches long were found to be efficient. A spiral of wire at ordinary temperature, if quickly dropped into the flame of an alcohol lamp, will extinguish it, see Fig. 754. A spiral of thick copper wire is suitable for the experiment. The alcohol flame is not extinguished by the exclusion of air as in an ordinary extinguisher, but because it is cooled down by the wire spiral. If the latter be heated before being introduced into the flame, it loses its extinguishing power.

If gas be lighted at a Bunsen burner or at an alcohol lamp, the flame from either of which will not deposit soot on objects in contact with them, and if a piece of fine iron wire-gauze about 6 inches square be held at one corner in the hand, first above and then lowered on to the flame, there is no appearance of flame above the gauze any more than there would be above a solid iron plate.