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AMERICAN SEA-GOING STEAMERS.

causing the boiler to become red hot; in this case, the water, when supplied, evaporates more rapidly than it can escape by the safety valve. In the Mississippi steamers, the paddle wheel shaft is so constructed, that the projecting portions of it on each side of the vessel can be thrown out of gear at pleasure, so that the shaft may revolve without producing any revolution of the wheels; by this means, when the vessel is stopped, the engines continue to work, and are employed in pumping water into the boiler.

(3.) The sea-going steamers of America are constructed on a principle which appears, to Europeans, insecure: there is a weakness in them, owing to the great proportion which their length bears to their breadth and depth. Dr. Renwick states, that "their length is as much as eight times their breadth of beam, and the form of their prows and sterns extremely acute: hence, the tendency to hog, and break their backs, is great; and one instance has already occurred, where a new vessel has gone to pieces by mere stress of weather. Vessels of this model are exposed to being washed from stem to stern by the waves." Another practice, adopted in sea-going vessels in America, is characterized by Dr. Renwick as a prominent mistake. "Departing from the practice which had become sanctioned by successful usage, of employing two engines placed upon the wheel guards, a single one has been substituted. This being necessarily placed in the plane of the keel, the rolling of the vessel is rendered more rapid, and more likely to be injurious. It is, indeed, a well-known principle in the stowage of vessels, that the rolling is to be rendered less violent by placing the weights at the greatest possible distance from the plane of the keel, as well as at the greatest height which is consistent with stability. The use of a single vertical engine of long stroke is attended with another difficulty, viz. that it requires a large opening to be left in the deck of the vessel, which cannot be sufficiently defended from the influx of the sea; for the bulk-heads which surround it, cannot be rendered strong enough to resist a violent wave." The first

steam boat which crossed the Atlantic, was the "Savannah," a boat built and equipped at the port of New York. This vessel proceeded, in 1819, from New York to Liverpool, without stopping at any intermediate port; she then went to St. Petersburgh, touching at Copenhagen; she then recrossed the Atlantic. It appears that steam was employed only during part of the voyage. Each trip was made in twenty-five days. The enterprise, thus undertaken by America, was successfully completed by the exertions of our own countrymen. In 1838, the "Sirius" performed the passage from Cork to New York in nineteen, and returned in eighteen, days. The "Great Western" left Bristol a few days after the Sirius, and reached New York in fifteen days, where the Sirius had arrived only a few hours before; she returned home in fourteen days. The average speed of this vessel was nine nautical miles per hour.

RECAPITULATION.

139. Who were the earliest projectors of steam navigation? By whom was the invention first practically applied? -140. In what respect does the mode of propulsion of a steam vessel agree with, and in what does it differ from, that of a land engine? What kind of engine is commonly used in steam vessels? What is the relative position of the beam and cylinders in land and marine engines, respectively? What is the proportion of the cylinders in each kind of engine?-141. Explain the general construction of a marine boiler. What object is secured by this mode of construction?-142. How is the thermometer employed as an indicator of the saltness of the water in boilers? What was the result of Mr. Dinnen's experiment on this subject? What is the principle of Dr. Lardner's contrivance for indicating

the saltness of the water in boilers? Explain the method adopted by the Messrs. Seaward for this purpose.—143. What is meant by blowing out? At what intervals is this process usually repeated? What is the object of brine pumps? How is the heat of the discharged brine economized?-144. How is the power of a marine engine estimated? What is the objection to this mode of estimation? What are the comparative advantages of a long, and of a short, stroke of the piston? What is the estimated velocity of the piston?-145. Explain the apparatus connected with the cylinder; the position of the beam; the action of the beam on the connecting-rod and crank; and the method by which both the beams of each engine act in propelling the vessel.-146. What mode of condensation has been generally adopted in the engines of steam vessels? What is the usual size of the condenser, relatively to the cylinder? How is the vacuum in the condenser ascertained? What are the usual proportions of the air-pump in marine engines? -147. What is the method of condensation adopted by Mr. Samuel Hall? What are the objects of his invention, as set forth in his patent?-148. Explain the construction of Hall's patent condenser.-149. Describe his distilling apparatus.-150. What is the plan of the steam saver?151-153. State the advantages which the patent engine of Mr. Hall possesses over the common injection engine.-158. What is the novelty in Mr. Howard's method of vaporization? What advantages are proposed by it? Explain his method of generating steam; and his process of condensation. What was the result of his experiment in the Comet"?-159. What are the usual dimensions of the valves and steam passages? Explain the position of the eccentric. Describe the apparatus of the expansive valves. -160. By what modifications of the engine may the expansive principle of steam be brought into more extensive operation?-161. Explain the causes which produce a loss of power in the construction of the paddle wheel.—162. What is the construction of Field's cycloidal wheel? What

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are the advantages, and disadvantages, of this contrivance? -164. Describe the general construction of Morgan's paddle wheel. What are the comparative merits of the paddle wheels already described?-165. How is the power of an engine affected by deep immersion of the paddles?—166. What is meant by a reefing paddle? What are the advantages obtained by Mr. Hall's patent reefing paddle wheel ?—167. To what circumstances is the success of the "Ruby" steam packet attributable ?—168. Enumerate the several parts of the marine engine, with reference to the plate of the frontispiece.-169. Describe the construction of the engines of the "Gorgon."-170. Explain the construction of the screw propeller.—172. What are the advantages of this mode of propulsion?-173. In what ratio does the speed of a vessel increase with increase of power?-174. What are the results of the experiments detailed by Mr. Barlow? What evidence do these experiments furnish of the relative economy of using Morgan's wheel and the common radiating wheel ?— 175. What are the further advantages arising from the principle on which these experiments were founded?—176. What are the advantages gained by the substitution of iron for wood, in the construction of steam vessels ?-177. In what respects did the engine of Fulton's first steam boat differ from that used in the present day? What rate of speed was attained by Fulton's boats? What was the form of his boats?—178. What improvements were introduced by Stevens ?What rate of speed was attained by his boats?— 179. On what circumstances does the great speed of the American steam vessels depend ?—180. How are the American steam boats classified? What are the peculiarities of the steam boats of the Hudson, and of those of the Mississippi? What are the defects of the sea-going vessels of America?