Such huge propellers as the _Majestic_ carries, and such great power as her engines develop, necessitate the use of heavy shafts, which are the great round steel rods that connect the engines and the propellers. These shafts run from the centres of the propellers through the ship’s stern to the engine room, and in the _Majestic_ are 16½ inches in diameter. Where they enter the ship there must be a very carefully built “stuffing box” and bearing which will prevent the entrance of water. Once each shaft has passed this bearing it runs for a considerable distance through a “shaft tunnel,” which is a long, low, narrow compartment through which men may walk in order to inspect the shaft and see that the bearings, which are spaced at intervals along the “tunnel,” are properly oiled. Finally the shaft reaches an apparatus called the “thrust block.” This is a simple but highly important arrangement. To explain its use it is necessary to go back to the propeller. When the engines are in motion and the propellers are being turned they develop a great “push” against the water, and it is this push that makes the ship move. If, however, something were not done to take up the push, the propellers would slide the shafts lengthwise through their bearings, and the end of the shaft attached to the engine would press so hard against it that it would push the engine from its base, or at least would wear the bearings out, and the engine would be damaged. In order to receive this “thrust,” as it is called, the “thrust blocks” are installed. There are several designs, but they all accomplish the same task in a similar fashion. [Illustration: THE _MAURETANIA_ _A British liner of the Cunard Line._] The shaft is equipped with a series of “collars.” These collars, which are enlargements of the shaft, are so placed that they fit between a series of surfaces attached firmly to a heavy fixed base, and when the propeller thrust tends to slide the shaft lengthwise, the “collars” press against these interposed plates which prevent the shaft from moving laterally without preventing its rotation. Naturally enough these thrust blocks must be lavishly oiled, for the friction between the turning collars and the fixed thrust blocks would otherwise soon wear both the collars and the blocks. When the propeller is reversed the thrust is against the other side of the collars, and so the engine is relieved of all duties save those of turning the shaft. When the shafts have passed these thrust blocks they have entered the engine room, which on these great liners is a place far different from the engine rooms on the smaller ships that are to be found the world over.