Like the boatmen of the Nile, the men who make these wooden habitations their usual dwellings are a distinct class. Launching their boats upon the Ohio, the Illinois, the Upper Mississippi, the Missouri, the Arkansas, and the Cumberland with all their respective tributaries, and guiding them to their final resting-place at New Orleans, these men are all known by the general designation of “Boatmen of the Mississippi.” They are a strong, hardy, rough, uncouth people, with a touch of the savage about them. [Sidenote: Engines.] Although the condensing engine is met with in some of the Mississippi steamers, high pressure engines are much more frequent, the pressure in the former being never less than 10 and frequently as high as 30 pounds to the square inch; when, however, this pressure is so worked, the object is to shut off the steam and take advantage of the expansion. In high pressure engines the pressure is used _ad libitum_ from 50 to 150 pounds, and, in former times, to such an extent, that no mortal was left to measure its height, the boiler as well as the boat and its contents, animate and inanimate, having too frequently been blown into the air. In condensing engines, when moving at full speed, the steam is never “wire-drawn,” as the engineers term it, the passages being made large enough, and the valves fully opened: the same, in high pressure engines: but, when not moving at full speed, the steam can be “wire-drawn” as the engineer thinks necessary. The term “high pressure” in America is applied to that description of engine which is worked against the atmosphere or without condensation; all condensing engines are called low pressure. In both these engines ashwood and pine, where coal could not be easily obtained, were the descriptions of wood most commonly used for fuel,[155] and, in the dangerous competition, happily less frequent now than it was some years ago, barrels of pitch, rosin, and even tallow were sometimes thrown into the furnaces, the recklessness of the captains and engineers on the Mississippi in working their boilers at a greater pressure than they could with safety carry, and, thereby, causing the frightful explosions to which I have just referred.[156] [Sidenote: Different construction of the steamers on the Atlantic rivers.]