Page:The Development of Navies During the Last Half-Century.djvu/283

 was the first of its kind supplied to the navy. The framing is entirely composed of steel, which has also been largely employed in the construction of the machinery throughout. The crank and other shafts are made of Whitworth special steel, and are all hollow. She attained a mean speed of 18.779 knots on the measured mile under unfavourable circumstances as regards weather, and has since then frequently achieved 19 knots on actual service. She has taken an active part in all naval manoeuvres of late years, and has been the terror of her imaginary foes, mainly because her engines have never broken down. This is no doubt owing to the fact that the stipulated weight of the machinery was exceeded.

The great difficulty in obtaining and maintaining high speeds in the navy has been the incapacity of boilers to withstand the strain put upon them. For this contracted dimensions have been mainly, and forced draught excessively and injudiciously applied, partly responsible. Forced draught is by no means to be wholly condemned. It is not, as Admiral Mayne called it, purely 'an invention of the Evil One.' But it requires to be used with care and judgment, when it will probably prove as valuable an auxiliary to the steaming power of our warships as it has undoubtedly shown itself to be in the mercantile marine. The 'Barham' and the 'Bellona,' sister ships, deserve a few words as to their machinery, which is very fin de siècle. They have each two sets of vertical triple-expansion engines, driving twin screws. The cylinders are 27 in.,