Turning now to the illustration of the turbine facing this page, let us see how this applies in actuality. This sketch represents a section of a cylindrical case with rows of inwardly projecting blades, and within this cylinder revolves a shaft with outwardly projecting blades. Steam enters at the point marked _A_ on the lower half of the cylinder, and then passes through the different rows of fixed and moving blades, as previously explained, finally leaving the cylinder at the exhaust pipe, marked _B_. But it will be noticed that the diameter of the shaft varies in three different stages, the reason for this being that a method analogous to the compound method in the triple-expansion engines is here employed. Thus the whole expansive force of the steam is not converted into speed all at one stage, but working its way along, expands as it goes. It should be added that the fixed blades are on the case of the cylinder, but the moving blades are on the rotor (or rotating part, consisting of a hollow steel drum), the steam rebounding from the fixed blades to the moving ones much as one billiard ball cannons off another. The cylindrical case is divided horizontally, and can be taken off, so that the blades may be got at. The illustration facing page 188 shows the lower half of the fixed portion or cylinder of one of the _Carmania’s_ turbines. The blades themselves are made either of brass or copper, and are caulked one by one into grooves in the cylinder and shaft, but a newer method enables them to be assembled in complete sectors ready for insertion. The Allan Line turbine-steamer _Virginian_ contains no fewer than 750,000 of these blades on the rotating part, but together with those which are fixed, they total a million and a half, the diameter of the largest blade being 8 feet 6 inches. Such, briefly, is the principle of the new form of engine which is causing so thorough an alteration in the means of propelling the steamship. Practically all the turbine craft are of the Parsons type. For some years this system was employed for driving electric dynamos on land, for pumping stations, colliery fans and the like, but in 1894 it was first installed in the now celebrated little ship, the _Turbinia_, which was built for the purpose of exhibiting the capabilities of the turbine. She was of only 44 tons, developing 2,000 horse-power, but those who happened to see her racing along the water at Spithead, doing her 34 knots without distress, were in no further need of conviction as to her speed abilities. But therein lay the drawback; the difficulty at first was to obtain such a speed as should be suitable for slow-going vessels, though we shall see that this difficulty is now disappearing. [Illustration: THE “CARMANIA” (1905). _From a Photograph. By Permission of the Cunard Steamship Co._] [Illustration: LOWER HALF OF THE FIXED PORTION OF ONE OF THE “CARMANIA’S” TURBINES. _From a Photograph. By Permission of the Cunard Steamship Co._]