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that a certain gas-light is equal to that of twelve sperm candles.

It will be recollected that the danger of permitting gasworks to be constructed in the metropolis was urged by the Committee of the Royal Society, appointed in 1814, who reported that such works ought to be placed at a considerable distance from all buildings; and that the reservoirs should be small and numerous. Amidst the success of the invention, however, these precautions seem to have been strangely disregarded. Thus, within a third of a mile, as the crow flies, of one of the largest Gas-works in London, are Westminster Abbey and Westminster Hospital; hard by are the Houses of Parliament, and groups of public offices. Milbank Penitentiary has but the river between it and the London Works; close adjoining is a huge holder. The Phoenix Works at Vauxhall are close to those of the London Company; at Bank-side are extensive works; and opposite are the Whitefriars Works, which threaten the crowded city, and its stupendous cathedral, St. Paul's. Explosions of appalling extent and destruction of life and property have occurred, an evil only to be provided for by the removal of the great works out of the metropolis ; to this the companies object, on account of the expense, although their profits enable them to divide 10 and even 20 per cent., besides a large reserve; and they tear up streets to the injury and annoyance of the public, even where subways have been made for gas and water pipes beneath the pavements.

The quantity of gas made by the several metropolitan gas companies is about 10,440,000,000 cubic feet per annum ; the gas sold may be taken at 9,000,000,000 cubic feet per annum. The difference between these quantities is the amount of the loss incident to the distribution; in fact, so much worse than pure waste, as it is injurious to health on being absorbed into the earth and expended in the air. The manufacture consumes nearly a million and a quarter tons of coal a year; the loss reqresents 1,440,000,000 cubic feet, which, at the mean cost of 4s. 8d. per thousand, is worth 336,000l. per annum, or a dividend of nearly 67. per cent. on the metropolitan gas companies, or 9d. per thousand feet on the cost of their gas. Yet, the West London Junction Gas Company has a meter at its works, and another three miles off, at the Great Western Station; and there is no difference between the quantities

registered by these meters, conclusively establishing that gas mains can be laid so as not to leak.

An explosion of gas is a terrific scene of destruction. On October 31, 1865, at the London Gas-light Company's works, at Nine Elms, Battersea-road, a gas-holder exploded, killing ten persons, and injuring twenty-two. This was one of the largest holders in London, its capacity being 1,039,000 cubic feet, though the Company have one which will hold 2,000,000 cubic feet. The former was 150 ft. diameter, 60 ft. high, with a tank depth of 30 ft., and at the instant of the explosion was nearly full, being about 50 ft. to 55 ft. high. The meter-house was blown to atoms, and the force of the explosion struck the side of the gas-holder, bulging it in, and at the same time driving out a portion of the top. As the side plates were eight to twelve wire gauge, the force must have been very great. With the bursting of the top there was an immediate rush of gas, which instantly caught fire, and shot up in a vast column of flame, discernible at a great distance. The concussion ripped open another gas-holder, the escaping gas caught fire, and meeting the flames from the first gasholder, rolled away in one vast expanse of flame: an awful crash followed, and many of the neighbouring houses were shattered to pieces.

Undoubtedly, the discovery of gas, and the application of it for the purpose of lighting our chief towns and cities by night, did as much good towards checking street robberies as the organization of the powerful Police-force. It is scarcely possible to overrate the importance of this invention, not only in an economical but in a moral point of view.

ARTESIAN WELLS.

HIS method of raising water by perpendicular perforations or borings into the ground has been named Artesian from the belief that it was first used in the district of Artois, in France; but the name appears to have been as well known in Italy as in Artois, from time immemorial. It is also probable that it was known to the ancients; for Niebuhr cites from Olympiodorus: "Wells are sunk in the oases from 200 and 300 to 400 yards in depth (the water being equal to half a foot), whence water rises and flows over." Through the Artesian borings the water rises from various depths, according to circumstances, above the surface of the soil, producing a constant flow or stream. They are highly useful in districts where springs or rivers are scarce, or where the usual surface-water is of indifferent quality. Their action is due to the constant endeavour of water to seek its level, and the principle is the same as that of an artificial fountain. Thus, imagine a somewhat basinshaped bed of sand, or chalk, or any rock of a porous nature, to lie upon a stratum of clay impermeable to water, and to be covered with another stratum equally impermeable. The former bed, being saturated to a great extent by the water which flows into it from its higher and exposed edges-a hilly region, perhaps, where rain falls in abundance becomes a reservoir, which, if an opening is bored down into it through the overlying clay, will discharge its waters upwards with a force determined by the level at which they are kept in the reservoir, the rate at which they can percolate through its substance, and the size of the orifice; and, in proportion as this reservoir is tapped by the borer, must the supply it affords on its upper margin be diminished.

As the water becomes impregnated with the various substances through which it passes, a general geological knowledge of the country in which Artesian Wells should be bored is indispensable: indeed, the power of pointing out these situations is one of the practical applications of geology to the useful purposes of life.

The operation of boring these wells is performed with chisels or jumpers, augers, and similar instruments, attached to the lower end of an iron rod formed of many lengths, which screw into one another. To the upper end of this compound rod is attached a transverse handle, worked by two men, by which the boring instrument may either be turned round, where an auger is used, or raised-turned a little way between each stroke; whereas, in cutting through rock, the hole must be formed more by chipping than boring. In boring through soft strata, a kind of cylindrical auger is used, which, when full of earth, must be drawn up and cleared; and a similar instrument is used to remove the chippings produced by the chisels employed to perforate rock. As the weight of the rods required for boring to a great depth would render them unmanageable by hand, a triangle of poles, supported by tackle for raising the boring rod is erected over the hole; and to facilitate the cutting or chipping through rock, the rod is suspended over the hole by a chain, from an elastic wooden pole fixed at one end only in a pile of stones. The vibration of this pole, when set in motion, gives the required up-and-down motion to the rod, while the turning of the transversed handle causes the chisel or jumper continually to vary its strokes. But there has been devised a boring instrument to be readily slid up and down the rod, so that the charged auger alone has to be raised, without disturbing a single joint of the rod.

One of the most celebrated Artesian Wells is that bored by the Messrs. Mulot at Grenelle, in Paris, which occupied 7 years, 1 month, 26 days, to the depth of 1794 English feet; or 1941 feet below the depth at which M. Elie de Beaumont, the geologist, foretold that water would be found. The sound or borer weighed 20,000 lbs. and was treble the height of the dome of the Hospital of the Invalides, at Paris. In May 1837, , when the bore had reached 1246 feet, 8 inches, the great chisel, and 262 feet of rods, fell to the bottom; and, although these weighed five tons, M. Mulot tapped a screw on the head of the rods, and thus, connecting another length to the end, after

fifteen months' labour, drew up the chisel! On another occasion, this chisel, having been raised with great force, sunk at one stroke 85 feet 3 inches into the chalk!

It is generally supposed that a provincial well-digger introduced into England the process of boring for water by the Artesian method, and that Tottenham was the site of the first boring, about 1822. The priority of the invention is, however, due to Mr. Benjamin Vulliamy, who, upon his estate of Norlands, at the foot of Notting Hill, bored the first complete and overflowing well by means of a tube. Mr. Vulliamy, who was a man of scientific repute, and a skilful mechanician, finished his arduous work in November 1794. He began to sink his well in the usual manner; it had a diameter of 4 feet, the landsprings were stopped out, and the well was sunk and steined to the bottom. When the workmen had got to the depth of 236 feet, thinking the water to be not very far off, they did not consider it safe to sink any deeper. A double thickness of steining was then made about 6 feet from the bottom upwards, and a borer of 5 inches' diameter was used. A copper pipe of the same diameter as the borer was driven down the bore-hole 24 feet, at which depth the borer pierced through the rock into the water; and, by the manner of its going through, it probably broke into a stratum containing water and sand. At the time the borer thrust through, the top of the copper pipe was about three feet above the bottom of the well: a mixture of sand and water instantly rushed in through the aperture of the pipe; and in less than an hour and a half the water of the well stood within 17 feet of the surface; it rose the first 124 feet in 11 minutes, and the remaining 119 feet in 1 hour 9 minutes. The boring was then found filled with sand to the depth of 96 feet, the removal of which was a work of difficulty, as was also the rebuilding of a portion of the brickwork; but at length the water ran over the top of the well.

The depth of the Grenelle Well is nearly four times the height of Strasbourg Cathedral; more than six times the height of the Hospital of the Invalides at Paris; more than four times the height of St. Peter's at Rome; nearly four times and a half the height of St. Paul's, and nine times the height of the Monument, London. Lastly, suppose all the above edifices to be piled upon each other, from the base-line of the Well of Grenelle, and they would reach within 11 feet of its surface.

Artesian Wells have, however, been bored of much greater

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