The truck is 24 ft. long and 16 ft. 41/2 in. wide; it is constructed of longitudinal and transverse box girders 2 ft. 8 in. deep, and rests on two axles 6 in. in diameter; round these axles swivel the cast-iron bogie frames which carry the ground wheels.  This arrangement was adopted because the crane has to travel up a gradient of 1 in 30, and the bogies enable it to take the incline better; they also distribute the weight more evenly on the wheels.  The gauge of the rails is 15 ft, the wheels are 2 ft. 6 in. in diameter, and have heavy steel tires.  The weight on each of the front wheels when running with the ballast, but no load, is about 16 tons.  A powerful brake is applied to the wheels when descending the incline.

All the clutch levers, break treadle, and handles are brought together, so that one man has the crane under his entire control.  An iron house, of which the framing only is shown, extends from the gearing right back to the boiler, forming a most spacious engine room and stokehole.  A separate donkey engine is provided for feeding the boiler.  The truck is furnished with legs under which packings can be wedged so as to relieve the load on the wheels when block-setting.  The slings seen under the boiler are for hanging a concrete balance weight; this will weigh about 20 tons.  The weight of the crane itself without load or ballast is about 80 tons.  The crane was tested under steam with a load of 19 tons with the most satisfactory results; the whole machine appeared to be very rigid, an end often very difficult to obtain with portable wrought-iron structures and live loads.  The result in the present case is probably greatly due to the careful workmanship, and to the fact that the sides and ends of the plates are planed throughout, so that the webs of the girders get a fair bearing on the top and bottom plates.

The crane showed itself to be very handy and quick in working, the speeds with 19 tons load, as actually timed at the trial, are:  lifting 16 ft. per minute, racking motion 46 ft. per minute, slewing through a complete circle 90 ft. diameter, four minutes, equivalent to a speed at load of 60 ft. per minute.  The crane was constructed by Messrs. Stothert & Pitt, of Bath, to the order of the Crown agents for the colonies, and we understand that the design and construction have given complete satisfaction to Sir J. Coode, the engineer to the harbor works, under whose supervision the crane was constructed.—­Engineering.

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IMPROVED STEAM-BOILER.