THE GENERAL ELECTRIC POWER AND TRACTION COMPANY, LIMITED. The works of the General Electric Power and Traction Company, Limited (late Immisch & Company), at Kentish Town, were visited. They comprise commodious and well-designed machine and erecting shops, pattern shop, drawing office, and smithy, and are specially adapted for the building of electric machinery. The company turn out both high and low speed machines for lighting, pumping, hauling, winding, etc., and they are also builders of steam dynamos and general mining plant. A number of machines for colliery work were seen in process of building or erection. Amongst other machines was a 100 horse-power dynamo, compound wound, designed for both electric lighting and motor driving, in the way proposed and elaborated by the company's chief engineer, Mr. Albion T. Suell, and described in the Transactions. Electric coal-cutting plant was also seen in course of construction.

The company's electric launch department at Hampton, and the section of the North Metropolitan Tramway Company's line at Barking, which is worked by the General Electric Power and Traction Company by self-contained electric cars, were also inspected.

THE LONDON ELECTRIC SUPPLY CORPORATION, LIMITED.

This company is possessed of Parliamentary powers over a large district, extending from Westminster Bridge to Greenwich on the south side of the river Thames, and Mayfair, Belgravia, St. James, Pall Mall, St. Martin's-in-the-Fields, part of Westminster, and the separated district of Clerkenwell on the north side of the river. The distribution is on the Ferranti alternating current system. The alternating current is generated at a high pressure and transmitted to converting stations, from which it is distributed to the service converters. The company has erected at Deptford a large and commodious central station, which is the largest generating station in the world.

The Grosvenor Gallery station, which is now closed, supplied about 38,000 incandescent lamps, which are now supplied from their Deptford station.

There are twenty-four boilers of the Babcock and Wilcox type, representing a total of 20,000 horse-power, but the boiler houses are constructed to contain boilers equal to the generation of 65,000 horse-power. Economizers are applied for the purpose of utilizing the waste steam by heating the feed-water.

The boiler house is arranged in two floors, and, with two engine houses, cover an area of 39,900 square feet, being 210 feet long by 190 feet wide, and have a height from basement to roof of about 100 feet. The engine houses are separated from the boiler house by a massive wall of masonry, and are each 195 feet in length by 66 feet in breadth, their height being 85 feet. A row of iron pillars separate the two engine houses and at the same time support the roof and the overhead travelling cranes, these latter being required for the lifting of heavy pieces of machinery.

Above the boiler house, forming a third story, provision has been made for the storage of 4,000 tons of coal. The coal, after having been unloaded on to the wharf, is hoisted to this storehouse, and, as occasion requires, distributed to the boiler houses by means of vertical shoots passing to the boiler fires.

The compound vertical engines are four in number, built by Messrs. Hicks, Hargreaves, & Co. of Bolton, two of them indicating 1,500 horse-power each: these drive two Ferranti dynamos by forty cotton ropes on each pulley. The other two engines indicate 750 horse-power each. Ample room has been provided for future extensions. The large Ferranti dynamos are capable of producing 25,000 lights of eight candle-power, and are 12 feet 6 inches high by 15 feet long over all. It is also intended to have three pairs of compound tandem engines, each pair capable of working up to 10,000 indicated horse-power at a speed of 60 revolutions per minute. The dynamo will be placed between the two engines forming the pair, with armatures 45 feet in diameter, the total weight of each machine being about 500 tons.

The dynamos being constructed will work at an E.M.F. of 10,000 volts, and the current, after being conveyed through concentric copper mains to London, is reduced to 2,400 volts at distributing stations. Underground cables run from these distributing stations over the City, and the current is again reduced to an E.M.F. of 100 volts for the purposes of public supply. Up to the present over 48 miles of mains have already been laid.

The Ferranti main is used for the transmission of the current, consisting of an internal copper tube conductor covered with insulating material, which is surrounded by an outer copper tube conductor. Special machinery has been erected for the manufacture of the Ferranti mains at Deptford. They are made in lengths of 20 feet. The inner conductor, consisting of a copper tube of square inch area, is placed upon a trestle and slowly wrapped with brown paper that has been previously dried upon a hot plate, and then passed through a bath of special black oil or wax, which soaks into the paper until the proper thickness of insulation is reached. The outer conductor, consisting of a copper tube of the same sectional area as the inner one, i.e.,square inch in area, is then slipped over the tube and insulation, and finally passed through a draw-plate so as to close the outer tube upon the insulation. The main is further insulated with waxed brown paper and taped, and a steel tube placed over the outside for protection. These 20-feet lengths of mains are joined together by suitable tapered tubes and sleeves of copper, so that a solid joint may be effected.

A considerable economy is effected in the cost of the copper conductors owing to the high tension at which the Ferranti system is worked, and there is only a loss of less than 3 per cent. by the use of these mains, which are capable of supplying 100.000 ten candle-power lamps each. The conductors are 2 inches in outside diameter, with a current density of 1,000 ampères per square inch section of copper.

NOTES ON THE SINKING AT THE LENS COLLIERIES, No. 10 PIT, BY THE POETSCH SYSTEM

BY N. R. GRIFFITH.

After the termination of the London meeting of the Federated Institution of Mining Engineers several of the members proceeded to the north of France to visit a shaft being sunk by the Poetsch system through water-bearing strata.

On their arrival at Lille they were met by M. Gobert, of 222, Chaussée de Charleroi, Brussels, the engineer in charge of the freezing arrangements, who accompanied them to Lens, where he introduced them to M. Reumaux, chief engineer of the Lens Collieries, for whom the shaft is being sunk, and then accompanied them to the shaft at Pont-à-Vendin, where every facility was afforded for the inspection of the operations in progress and the fullest information on all points was given by M. Gobert.

The shaft had been commenced on the ordinary method of sinking about two and a half years previously, and sunk in this way about 84 feet, when it was found impracticable to proceed further in this manner, partly on account of the enormous quantity of water met with, which pumping appliances of 1,000 horsepower were insufficient to cope with, and partly on account of a portion of the shaft, which portion had been lined with timber, having been crushed in. (Fig. 1, Plate XLI.)

Of the ground passed through, the upper portion consisted of quicksand and the lower of chalk.

As some of the permanent surface arrangements had been erected, the Lens Company, instead of abandoning the shaft and commencing a fresh one elsewhere, decided to try to put the shaft down through the water-bearing strata by the Poetsch process.

The shaft is 15 feet 9 inches diameter in the clear, and when operations on the Poetsch system commenced was full of water to the natural level of the water in the ground close to the surface. The operations on the Poetsch system, which had been carried out before the visit of the members of the Federated Institution were as follows:-Inside the shaft eight boreholes (Fig. 2, Plate XLI.) were put down to a depth of 137 feet 9 inches from the surface. Outside and surrounding the shaft twenty boreholes were put down to the same depth, at which there is a bed, which it is believed will form a good foundation for the permanent tubbing.

The boreholes were put down in the ordinary way, and lined temporarily with sheet iron casing about inch thick, commencing with 14 inches diameter, decreasing to 10 inches diameter, and, finally, to 8 inches diameter.

Inside each borehole, when finished, was placed a flush-jointed wrought iron tube, 4 inches diameter, closed at the bottom end, and inside each of these tubes 3 G

VOL. II.-1890-91.