But it was not in its consumption of fuel alone that stationary power was the more economical; the expenditure in wages, oil, and tallow on one of the pumping-engines above referred to, when doing 200 horse-power of useful work, did not exceed 20_s._ for the twenty-four hours, or one-twentieth of a penny per horse-power per hour, while the cost of repairs was merely nominal. Thus if fuel, wages, oil, and tallow be brought into one item, it is seen that the cost of one horse-power in stationary engines such as the then existing Cornish engines was only ·25_d._ per hour, or less than one-fourth of its cost when developed by a locomotive, which has been shown to have been 1·098_d._ per hour. [Illustration: PLATE III THE ROYAL ALBERT BRIDGE. H. Adlard. Sc.] CHAPTER VII. _RAILWAY BRIDGES AND VIADUCTS._ 1. BRICKWORK AND MASONRY BRIDGES--HANWELL VIADUCT--MAIDENHEAD BRIDGE--FLYING BRIDGES--LETTER FROM MR. BRUNEL ON BRIDGE CONSTRUCTION (DECEMBER 30, 1854)--2. TIMBER BRIDGES--SONNING BRIDGE--BATH BRIDGE--STONEHOUSE VIADUCT--BOURNE VIADUCT--ST. MARY’S VIADUCT--VIADUCTS ON THE SOUTH DEVON RAILWAY--IVY-BRIDGE--VIADUCTS ON THE SOUTH WALES RAILWAY--NEWPORT--LANDORE--VIADUCTS ON THE CORNWALL RAILWAY--ST. PINNOCK--VIADUCTS ON THE WEST CORNWALL AND TAVISTOCK RAILWAYS--PRESERVATION OF TIMBER--3. CAST-IRON BRIDGES--LETTER ON USE OF CAST IRON (APRIL 18, 1849)--HANWELL BRIDGE--EXPERIMENTS ON CAST-IRON GIRDERS--EXTRACT FROM LETTER TO SECRETARY OF COMMISSION ON APPLICATION OF IRON TO RAILWAY STRUCTURES (MARCH 13, 1848)--4. WROUGHT-IRON BRIDGES--GIRDER BRIDGES--EXPERIMENTS ON WROUGHT-IRON GIRDER--OPENING BRIDGES--TRUSSED BRIDGES--NEWPORT VIADUCT--WINDSOR BRIDGE--CHEPSTOW BRIDGE--METHOD OF SINKING THE CYLINDERS--DESCRIPTION OF THE MAIN TRUSS--THE FLOATING OPERATIONS--THE ROYAL ALBERT BRIDGE AT SALTASH--THE CENTRE PIER--DESCRIPTION OF THE SUPERSTRUCTURE--THE FLOATING AND RAISING OF THE TRUSSES--OPENING OF THE BRIDGE BY H. R. H. THE PRINCE CONSORT--_NOTE_: EXPERIMENTS ON MATTERS CONNECTED WITH BRIDGE CONSTRUCTION. In Chapter IV. a general history has been given of the railways of which Mr. Brunel was the engineer; but the bridges and viaducts designed by him are so numerous and important that it has been thought advisable to devote a separate chapter to their consideration. The bridges selected for mention have been grouped according to the nature of the material used in their superstructure. This arrangement is the most convenient one for giving a concise description of the most remarkable of Mr. Brunel’s bridges, and for stating the circumstances which guided him in the determination of the particular form of construction used in each case. The works are therefore divided into four groups, namely, brickwork and masonry, timber, cast iron, and wrought iron.[77] _Brickwork and Masonry Bridges._[78]