and there built in, the whole being carefully levelled. After the wall is completed the cantilever pieces are sawn off, and if the appearance of the ends be deemed unsightly, they are cut out of the wall for an inch or two and the face floated over.

In the second method (fig. 39) long timber uprights are arranged at regular intervals. At each side of the uprights is a groove, within which a mould can slide up or down as required. When raised to each fresh position, it is temporarily secured by wooden wedges.

In every case the surface of a concrete mould should be coated with a suitable oil, or greasy preparation, to minimise adhesion.

Block-setting Appliances. -For the purpose of dealing with massive concrete blocks, used for construction in exposed situations, two types of appliances are generally employed, known by the generic titles of Goliath and Titan respectively.

The Goliath is an overhead traveller, with rectilinear motions. The frame, consisting of two vertical sides connected by an upper horizontal platform, travels backwards and forwards upon two lines of rails at the ground level. The platform supports a track for the transverse motion of the hoisting machine. The general function of a Goliath is the removal of the blocks from the moulds, in which they have been formed, to the stacking. yard. An illustration of one is given in fig. 40, which represents a 42-ton steam Goliath, constructed by Messrs. Ransomes & Rapier, of Ipswich, for harbour work at Dover. The span of the main girders, which are 138 feet over all, is 100 feet 1 inches between centres of tracks, and the clear headway is 25 feet, while the total lift is 120 feet. The speeds of the various movements are:-Lifting, 10 feet; crab travel, 50 feet; main travel, 60 feet per minute. The weight of the machine in working order is 216 tons.* The Titan is also an overhead traveller, but on the cantilever principle. which admits of rotary as well as rectilinear motion. Its function is to take the blocks from the yard and deposit them in their places. The earlier type of Titan did not possess the turning movement, but this latter is very useful in setting apron blocks alongside the main work. The Mormugao

⚫ Engineering, September 29, 1899.

machine, constructed by Messrs. Stothert & Pitt, of Bath, illustrated in fig. 41, used for constructing a breakwater at the port of Goa in India, is of this kind. The overhang is 25 feet, measured from the front leg to the extreme position of the load; the extreme range of cross travel is 18 feet and the vertical range of lift 40 feet; the clear height under the cross girder is 163 feet and the working load 40 tons.*

Excavators.-The various classes of implements for the removal of earthwork, in bulk and in the dry, from the site of a proposed dock may be enumerated as

Land Dredgers.
Steam Navvies.
Grabs.

Land Dredgers are an adaptation of the principle of sea dredgers to land. work. They are a foreign product, and subdivisible into two types, which may be distinguished as the French and the German respectively, according to the country of their origin. Both, however, are one in mode of action, and the distinction between them simply lies in the fact that the former discharges its load into waggons entirely to the rear, while the latter discharges into waggons which pass underneath its framing. This arrangement gives the German machine a wider base and greater stability. There "Plant for Harbour and Sea Works," Min. Proc. Inst. C.E., vol. cxiii.

*Pitt on

are occasions recorded in which the French machine has overturned when working in light, marshy clays.

While the principle of the land dredger is identical with that of the sea dredger, there is a difference in the method of working. In the sea dredger the buckets excavate downwards, away from the vessel, whereas in the land dredger the cutting action is upwards, towards the machine. The buckets of a land dredger are much shallower and lighter than those of a sea dredger, but both machines are alike in that they are fitted with two tumblers, about which the buckets revolve, discharging their contents in passing over the upper tumbler.

A very important advantage attaching to the use of land dredgers is the saving of a considerable amount of haulage up inclines. The machines not only excavate cuttings to a depth of 15 or 20 feet, but they also deliver the spoil at a level of 6 or 8 feet above the ground upon which they travel. This means, of course, a marked saving in time, as well as in locomotive or winding power.

On the other hand, the first cost of these machines is very great, amounting to about £2,400 each; and they require much heavier roads than machines of lighter build. Under very favourable circumstances the cost of excavation with these machines has amounted to 1d. per cubic yard excavated, but this figure may very easily be doubled in cases where space is circumscribed and action impeded. Such conditions often prevail in dock construction.

French Machine.- A land dredger constructed by Messrs. J. Boulet et Cie., of Paris, is illustrated in figs. 42 and 43. It was employed in excavating the site of Canada Branch Dock No. 2, Liverpool, and formed one of four engaged upon the formation of the Manchester Ship Canal. Experience showed that it is only suitable for use in connection with light soils, such as earth filling, sand, loam, and gravel. It is of no value in stiff clay or in rock, however soft. Being heavy in build (about 80 tons weight), a strong and expensive road is entailed to carry the machine upon the soft ground in which alone it is effective. For this purpose steel rails, weighing 80 lbs. per yard, are required, resting upon cross sleepers 2 feet apart, and sometimes upon longitudinal sleepers in addition.

Another important consideration is the fact that a special locomotive is required in attendance upon the machine to move the waggons along under the discharge shoot, as, although the excavator has motive power, it is not sufficiently rapid to keep pace with the rate of filling. About forty men are also required to be in attendance, tending and laying the road.

At the Canada Branch Dock the French machine has excavated 770 cubic yards of soft material in a day of ten hours, and its average has been 600 cubic yards per diem, but the area in which it worked was restricted and the material not altogether favourable, so that it did not