have a fair chance of displaying its maximum capabilities. On the Manchester Ship Canal, where there was much greater scope, Sir E. Leader Williams records the following as being the best single-day performances on different sections of the work :*-No. 3 section, 1,943 cubic yards; No. 5 section, 1,624 cubic yards; No. 7 section, 2,250 cubic yards; No. 8 section, 2,025 cubic yards. "These," observes Sir Edward, "are remarkable figures; but the soil and other circumstances must be suitable in order to afford such results. The average day's work on all the districts was about 1,500 cubic yards. If 440 waggons, containing 1,650 cubic yards, were filled per day on No. 8 section, it was considered a fair day's work. A bonus of a penny per cubic yard was paid to the men on everything above this quantity. For the excavation of this quantity the average daily expenses of the machine in wages of crew, coal, stores, and repairs, the last item being heavy, were about 60s., or 0.44d. per cubic yard excavated. There were employed upon the excavator an engine-driver and a stoker, and, round it, a number of men, varying from 28 to 43, the average number being 35, the roads requiring frequent moving."

German Machine. The land dredger, illustrated in figs. 44, 45, and 46, was made by the Lübecker Maschinenbau-Gesellschaft. Similar in principle and in mode of action to the French machine, it will only be necessary to touch upon the points of difference, which are of but secondary importance. The German excavator has greater stability, owing to its broader base, and its motive power is sufficient to propel it forward at a rate commensurate with the speed of filling the waggons; hence, an attendant locomotive is unnecessary. The machine is some 10 tons less in weight than the French machine, and is generally of lighter build, but the initial cost is about the same. The following particulars of its work upon the Manchester Ship Canal are taken from the paper by Sir E. Leader Williams already referred to :—

"The best day's performances that are recorded in its favour are as follows:-No. 3 section, 2,073 cubic yards; No. 4 section, 1,736 cubic yards; No. 5 section, 1,725 cubic yards; and No. 6 section, 2,400 cubic yards. The average day's work is 1,416 cubic yards, with an average number of 36 men. The average daily expenses of the machine in wages of crew, coal, stores, and repairs are about 60s., or 0·5d. per cubic yard excavated, which is increased to 16d. per cubic yard by the wages of the labourers who attend on the excavator."

Summarising the results of experience in the working of land dredgers in England, it may be said that in light material and on level ground they will fill waggons at considerable speed and with economy; and where large excavations of soft material have to be made with rapidity, the bucket dredging system gives the cheapest and best results. But they

* Williams on "Mechanical Appliances employed in the Construction of the Manchester Ship Canal,” Min. Proc. I. Mech. E., 1891, p. 418.

will not excavate heavy or strong material; they are difficult and expensive to maintain, and therefore cause delay to the work; they require a costly and a heavy road, and special precautions on soft ground to prevent them from tilting over into the cutting; and they are expensive to move from one cutting to another."

Steam Navvies represent a class in which excavation is performed by a single bucket working at the end of an arm or lever. The machines travel along the bottom of the cutting, and the mode of action is an upward curved sweep of the bucket against the face of the ground in front. Steam navvies or excavators, as they are sometimes called, are characterised by great power. They are capable of working in the stiffest clay and the hardest marl. They will also take soft rock unaided, and hard rock with the assistance of a little blasting.

The Ruston Steam Navvy, manufactured by Messrs. Ruston, Procter & Co., Ltd., of Lincoln, has a strong spandril-shaped jib, intersected at its centre by a long arm, at the lower end of which is the bucket. The arm is capable of forward motion by means of rack and pinion gearing, and it also rotates about the pinion under the tension of a chain leading from the bucket to the head of the jib. The method of action is clearly indicated in fig. 47. The size usually employed for dock work is that developing 10 H.P., in which case the capacity of the bucket ranges from 14 cubic yards for stiff ground to 2 cubic yards for sand. The best results are obtained when the excavation has a depth of from 20 to 25 feet. Under such circumstances from 1,700 to 2,000 cubic yards of sand, and very dry, friable material, have been obtained in a day of 10 hours, but a fair average in mixed earth, under ordinary conditions, would be 600 to 700 cubic yards per diem. In hard material, such as rock and rocky marl, the output is necessarily less again than this. At Barry Docks from 450 to 500 cubic yards per day were excavated, the marl being first loosened by powder. Of soft material, 1,000 cubic yards were obtained in a single day, on several occasions, at the same place.

The disadvantages attaching to the machine, undoubtedly powerful and useful though it be, are its great weight (about 45 tons), which necessitates a very solid road, and its inability to work otherwise than directly forward. The waggons to be filled must be ranged alongside, as the pivot only rotates through a semicircle, and a wide base is required to accommodate two waggon roads in addition to the navvy road. The first cost of the machine is about £1,200, and the working expenses, including wages, amount to about 30 shillings per day.

The Simpson and Porter Excavator (fig. 48), manufactured by Messrs. J. H. Wilson & Co., Ltd., of Liverpool, is a lighter machine, but very effective in suitable soil. The special point in its favour is its ability to revolve through a complete circle, and therefore to deliver the excavated material into waggons at its extreme rear, if necessary; and further, by disconnecting the bucket gear, the machine is readily available for use