(Continued from page 67.) In every dissertation upon machinery, the ubject of first importance to be discussed is he Steam Engine and we shall accordingly egin our remarks upon its present condition, vith that powerful auxiliary to man. It is lot here the place to descant upon the utility f the Steam Engine, nor write the biography if its improver—James Watt—both are alike ppreciated—the Mechanic and his work— loth have been the theme for the pen of many iistinguished writers, and both will go dowr 0 posterity in joined remembrance—the Ope-ative and his labor, the Steam Engine and rames Watt. To give a history of the Steam Engine hrough its progressive improvement, would )e a subject of interest, but would require a greater extent of space than can be here af-orded for it, besides, so many books have beer written upon the subject that any such ac-:ount could be only a repetition of what has )een already said. We shall, therefore, omit he usual prefatory remarks, and proceed di-ect to the subject that we propose to trea1 ipon, Damely, the Steam Engine in its presen' tate. This, tor the better convenience ot per-ipicuity, we shall classify under three heads iz.. Marine, Land, and Locomotive—a divi-jion that is generally employed by the bes writers upon the subjdct. Marine Engines—In adverting to the Ma- ine Engine, we at present more particularl] lUude to the species of engine employed ii jea-going vessels, which differs considerabl] Tom those employed on our rivers and lakes and even along the sea-coast, as in the instanci jf the steamboats which traverse Long Islanc Sound. The form of these last-named engines ilthough well adapted for tranquil waters would be found unfitted for the stormy ocean The description of engine used for sea-goinj vessels is generally known by the name of th marine condensing engine. For many year the side-lever engine alone was employed fo 3ea although modern practice has, for som bime past, earnestly sought to introduce i more compact shape. It is, indeed, customar for many to speak of the side-lever engine a a thing of the past, and as bemg entirely su perseded by direct-action engines. A littl reflection, however, will show that many c our best vessels are still furnished with ma chinery of the side-lever description, and al though we feel strongly the many defects c this variety of engine, it cannot be denies that several of its substitutes have proved sti] worse. There are, however, other direct-ac tion engines which are decidedly superior,an we trust that the inventive genius of our cour trymen will add still further to the numbe: A few of the best direct-action engines we ir tend, briefly to describe, but will first glanc at the side-lever engme. Side-Lever Engineka engine ot this fori may be thus briefly described :—On a stoi bed-plate is fixed the cylinder, behind whic are the condenser and air-pump, all three be ing ranged one atter the other in a line wit the length of the vessel. On either side of tt cylinder is one of the side-levers, which give the name to this variety of engines. Thes levers are, in tact, beams not exactly shape like those in our river steamers, the propo: tionate depth being much less, and being als formed in one mass; in fact they approac closely in shape to the beam as made t James Watt. It is said that the side-lev* engine owes its origin to a rival of Watt, wh irritated by the praises Jestowed on the a rangement as planned by his competitc boasted that he could turn that arrangemei upside down, and yet make the engine wor This he seemingly effected by placing tl beam at the foot of the cylinder, in which pi sition it is generally called a side-lever. It certain that this disposition of the beam most advantageous for insuring the stability thft vessel, and accordingly, for a long peric it was the only mode employed for sea-goii vessels, but when the length of the voyaj was extended, and it was requisite to rend available all possible space, it was then foui that the side-levers occupied far more roo than could be afforded. To this defect mi be added the great weight of the side-leve or sway-beams (which, however, is much le than formerly, as they are now usually made of wrought-iron), the friction on the main centres on which the beams work, and the strain on the foundation plate. We have mentioned the faults of this engine, but it has an advantage over many of its direct-action competitors, in permitting the use of a long connecting-rod, which is of more importance than may at first sight appear. That a vast field is open for improvements in the marine engine, will be evident when we reflect that a first-class locomotive will exert a power equivalent to one thousand horses, and yet will weigh but 35 tons, including the water in the boiler, thus giving 30 horse-power for each ton of its weight. Now, the side-lever engine, with the flue-boiler in use a few years ago, gave only a force of two horse-power for each ton weight of the engine and boiler. The present direct-action engine, with tubular boilers, gives from four to sixhorse-power for each ton. This is certainly a great improvement, but the instance of the locomotive cited above, points to further progress, at the same time we must remember that the latter is a high-pressure engine, and, consequently, the addition of a condenser, air-pump, hot well, &c.5 does not increase the aggregate of its weight. The former vessel has remained nearly the same inconstruction since its first employment, and offers a wide scope for improvement. To condense the steam rapidly and effectually, is the desideratum to be obtained, and which must be done in the smallest space possible. Some attempts have been made to improve the condenser by fixing a number of tubes within it, thus exposing more surface to the effects of the cold water. This system at one time found great favor, but has tallen into disrepute, owing to the exceeding trouble and consequent expense of keeping the tubes ir proper order. (To be Continued.)