built of steel. It may be added that she was also the first vessel wherein the construction of her machinery was much hampered by considerations of weight, and as a consequence in her engines were introduced, for the first time, hollow compressed steel shafts, invented by the Whitworth firm. The engines, by Messrs Maudslay, were indeed of a type entirely new to the navy. The firm had obtained considerable credit and renown by the extraordinarily fast passages made by the 'Germanic' and 'Britannic,' Atlantic mail steamers engined by them for the White Star line. The compound engines of the 'Iris' are exactly on the same principle, but horizontal instead of vertical. There are two distinct sets, driving twin screws, and each set has four cylinders, two high-pressure at the back of the two low-pressure ones, arranged in what is known as 'tandem' fashion. ‘The narrow beam of the ship, in proportion to the size and power of the engines, rendered it necessary to place the starboard engine in front of the port engine, so that the whole body of the ship is filled with machinery.’ So says Lord Brassey, but what was considered an exceptional case in 1876 is now the universal order of things.
The 'Iris' carries 500 tons of coal in the ordinary bunkers, and 250 tons additional in the reserve bunkers. The total weight of the machinery, with water in the boilers and condensers, is about 1000 tons, and the contract price was £93,000. From the Times account of her trials we learn that she proved to be not only the quickest ship in the navy but the quickest ship afloat
