This quality results from the fact that each end of the boat forms a tank, which is filled with water, and as there is no extra buoyancy in those directions, and consequently no tendency to lift at those parts as with an ordinary vessel in a sea-way, the vessel rises and falls bodily instead of pitching. It has been found that by going at a moderate speed and taking the seas a point or so on the bows the boat makes very good weather, as the waves, breaking on the snout, sweep over the fore part and expend their force before any portion of them can reach the central section. Steam, which is employed as motive power, is perfectly trustworthy as an agent. There is nothing about its action, or the appliances connected with it, that is beyond the grasp of an ordinary engineer, whereas such can hardly be said as yet in respect either to electricity or the other agencies by which inventors have sought to obtain motion. The difficulty, however, has always been how to retain steam pressure for any great length of time without carrying on combustion. This in the Nordenfeldt boat is secured in the following ingenious manner: A large reservoir or hot-water cistern (marked Q in the plate) is placed in the fore part of the boat, in communication with the boiler. The steam from the latter passes through a number of tubes in the reservoir N, thus raising the temperature of its contents until the pressure stands at the same degree in both. While the boat is at the surface, the maximum pressure once attained, as long as combustion is carried on, supplies quite enough steam both for driving the engines at full speed and for maintaining the contents of the cistern in the proper superheated condition. When the boat is submerged and the furnace doors are closed combustion ceases, and the steam given off by the hot-water in the boiler and cistern is sufficient to keep the engines going for several hours. [Illustration: LONGITUDINAL PLANS OF NORDENFELDT BOAT.]