algebraically, the elements of the formula can be recorded against the performances of the ships, and definite conclusions may be drawn. Thus, when the spread of canvas, its position on the spars, the pressure of the wind, coupled with the results in tacking and scudding, shall have been observed for ships of different formulæ, we shall be able to make up what are called equations of condition, by help of which the best forms for general service or for particular destinations may be safely determined.

Nor need the first experiments be made at haphazard; we can take, as our starting-point in the race of improvement, the very best models that have hitherto been found, while the essays at amendment may be made with the utmost caution, since we can alter the data of our formulæ by the most minute quantities.

I do not think that I am over-sanguine in expressing the hope, that the adoption of the sefinet method may soon change naval architecture, from being a business of mere taste and guess-work, to be a branch, and a very important branch, of exact science.

On the Risca Colliery Explosion. By RALPH MOORE,

M.E., of Glasgow.*

On the morning of Saturday the 1st December last, an explosion of fire-damp occurred in the Black Vein Seam of the Risca Coal and Iron Company's Works at Risca, a village seven miles north from the shipping port of Newport, South Wales, whereby 142 persons out of 200 were killed. At every recurrence of those disasters, involving, as they do, the loss of life and property, public attention is strongly directed. to them, and there usually follows an amount of correspondence in the public papers, comments upon the disaster, suggestions for relief of the sufferers, and remedies for the prevention of such accidents.

While a great proportion of these are unsuitable, it cannot be denied that some of them contain useful information; and that, at all events, the tendency of them is to do good. The

* Read before the Society, and drawings exhibited, 25th March 1861.

suggestions of scientific men are always valuable, but if their attention was directed by practical men to the details of the circumstances which caused the explosion, instead of collecting them from the imperfect accounts in the press, they could scarcely fail to be more valuable.

With the view, then, of bringing before the Society the facts necessary to elucidate an explosion of fire-damp in a mine, the writer has endeavoured to collect and put into shape the various features of that which occurred at Risca, in the hope that he may be able to explain the subject, so that scientific men may point out some department where science can be brought to bear on behalf of the poor miner in his dangerous toil, and to insure to the capitalist greater security for the property he may have at stake; for while the general sympathy goes with the persons who are injured, or with the relatives of those who are lost, we must never forget that the proprietor of the mine is not an inconsiderable sufferer,—indeed, it often happens, while he has to bear his loss in silence, he has in addition very frequently to bear an amount of unmerited obloquy.

All mines give out, more or less, two inconvenient products, gas and water; gas issues from the pores of the strata, as the fresh surfaces are exposed, and if it is allowed to accumulate, becomes injurious or dangerous to those coming in contact with it. These gases are carburetted hydrogen, and carbonic acid, although other gases may exist, such as, for instance, sulphuretted hydrogen, from the decomposition of the iron pyrites. If carbonic acid gas or choke-damp be emitted, it is hurtful, and often fatal, even if forming only 5 per cent. of the surrounding atmosphere which the miner breathes; and if existing in a greater proportion, it prevents his light from burning, and thus gives timely warning for him to leave. If, on the other hand, the gas present be carburetted hydrogen, or fire-damp, from 6 to 20 per cent. of it mixed with common air produces an explosive mixture, which in an unguarded moment comes upon the miner's lamp and causes these fearful explosions which we hear of from time to time, and of which that at Risca is a prominent instance. Both the water and the gas, however, must be got rid of. The water must be completely drained. The means must be complete; a level by

which it may discharge itself, or a steam-engine proportioned to the quantity of water to be raised, must be provided; if small, the engine is small,—if large, the engine is large, and so must also be the expense; and the capitalist counts the cost and acts accordingly, for it must be done to insure admission into the mine at all. Wherever the miners work, there must be no water.

With gas, matters are different. Gas does accumulate, but only to a certain extent will it find its level-it may to a certain extent be kept within bounds; and hence, when the machinery or arrangements for the withdrawal of all the gas are incomplete, we find devices for keeping only that part of the mine where the workmen are engaged clear of gas, and hence, also, the frequent carelessness and inattention to the ordinary means for its adequate removal.

I purpose, in the first place, to narrate shortly the usual mode of ventilating mines; next, to show the position of matters at Risca, the mode of ventilation adopted, the manner in which it was carried out, and the effect of the explosion; then to offer some suggestions for improvement; and, lastly, to suggest a mode of providing for those deprived of the means of subsistence by these catastrophes.

The mode adopted for clearing away the noxious gases from mines, is to send through the mine such a quantity of atmospheric air as shall sweep away, or dilute them to such an extent. that the workmen may enter with safety; and the art of ventilation consists in sending down sufficient atmospheric air to support the respiration of the workmen employed, the combustion of their lights, and to carry off the obnoxious gases referred to. The quantity of air necessary depends upon the size of the mine, the number of men employed, and especially the amount of gas eliminated; but there ought always to be a surplus; and in a properly arranged colliery, the cost of ventilation forms but an inconsiderable item in the general expenses. The quantity varies from 4000 or 5000 cubic feet per minute to 200,000 cubic feet per minute. Few of our Scotch mines require more than 10,000 feet per minute, the average will not be 6000, while the "Hetton Colliery" requires 200,000 cubic feet per minute. To illustrate this more forcibly, a

current of air passing through a common door-way, 7 feet by 3, at the rate of 2 feet a second, or a mile and a half per hour, will be required on an average to ventilate Scotch mines; while to ventilate the Hetton mine in the county of Durham, it would require to blow at the rate of 166 feet a second, or upwards of 100 miles an hour; or suppose this hall to have a sectional area of 600 feet, Hetton air-currents would pass through it at the rate of 5 feet a second, or more than 3 miles an hour. In the case of Risca, to which I am about to refer, the current of air passing was 40,000 cubic feet per minute, about one-fifth of the quantity at Hetton, and it would pass through this hall at the rate of four-fifths of a mile per hour. The opening through which the air descends from the surface into the mine is called the "downcast" shaft, the lateral passages to the faces are called the "intake" air-courses, those by which it returns are called the "return" air-courses, and the shaft through which it ascends to the surface is termed the "upcast" shaft.

The current of air is created by artificial means, sometimes by a fall of water in the downcast pit, but more commonly by an exhausting apparatus, such as fans, air-pumps, the steamjet, or a rarefying furnace, the last being the most usual.

The amount of exhaustion thus created is from nothing up to four inches of water, or 20 lbs. pressure per square foot. When the furnace is used the exhaustion never comes up to 2 inches of water. The amount of ventilation should be sufficient to have every portion of the mine thoroughly saturated with pure air, and in proportion as this is thoroughly accomplished, is the state of the atmosphere of the mine.

We will now be prepared in some measure to understand the state of matters at Risca, at the time of the explosion there, and as shown on the accompanying plan, Plate III.

The establishment for working the "Black Vein" of coal at Risca consists of three pits,-first, an upcast shaft " No. 2 Black Vein pit" to the rise, used solely for ventilation, eggshaped, 16 feet long by 10 wide, having an area of 125 square feet, and 70 yards deep; next, about 400 yards to the dip, a winding shaft of the same dimensions 148 yards in depth, "No 1 Black Vein pit" forming the downcast; and thirdly,