184G.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



381 



and equal weight of metal, with those of England. These steamers, being 

 of the classes which 1 propose, could never be blockaded in our ports by 

 the existing naval means of any country. Moreover, if maintained in sufii- 

 dent numbers, so as to be readily assembled in large squadrons at the 

 pcnnts where the exigencies or demands of the service iiiight require, the 

 most powerful fleets would be unable to maintain a blockade, or to carry 

 out with success a military expedition against our shores. 



The same classes of steamers are also of esseniial importance on our 

 frontier lakes, where armed steamers of the heavy classes and draft of 

 water hitherto adopted, would be of greatly inferior value; and where all 

 the strategetical advantages will be in favour of the classes proposed. 



The greater value and adaptation of light built steam vessels, tenaciously 

 constructed — not less in lengtii and size, uor exceeding in weight and draft, 

 the average of the classes C and D, may be now reviewed, or more sum- 

 marily considered.* 



I. Their facility of movement and surpassing speed, exceeding that of 

 existing war steamers from three to six miles an hour, must necessarily 

 atTord, as above mentioned, the choice of action and position ; and except- 

 ing accidents, no enemy can either escape or overtake them, except at the 

 will of their commanders. 



II. Owing to the light draft of water and greater speed of these vessels, 

 they may shelter themselves from a superior force in shoal positions, or 

 attack and annoy the enemy from such positions on a vast extent of coast 

 and inner waters, where heavy ships or steamers cannot approach. M hen 

 the elaborate survey of our coast, now in progress, shall have been com- 

 pleted, and our officers shall also have become familiar with these shallow 

 grounds by active co,ist service, in proper steam vessels, these facilities 

 may become of great value. 



Hy this means, not only may the exposed positions at Key West and 

 oJher points be maintained in war, and made available for the annoyance of 

 an enemy, but the strait of Florida, if not the other outlets of the Caribbean 

 Sea and Gulf of Mexico, maybe effectually and securely blockaded by 

 squadrons of these steamers. 



By means of these active steam vessels, and a suitable and skilful force 

 of marines and marine artillery, trained for both land and sea service, 

 which, 1 trust, may shortly be provided, an enemy's colonial posts may be 

 captured, and his military resources laid under contribution. By like 

 means, in case of a war with England, might the coal furnishing ports, 

 and other outposts near our eastern frontier, be taken into our possession, 

 and retained, or abandoned, as occasion might require. 



It is chiefly by these means that we may expect to command, in such 

 emergency, the more hazardous coasts of Maine, Nova Scotia, and the Gulf 

 of St. Lawrence; thus cutting olf the communication and niililary supplies 

 uf an enemy, and virinally blockading his American colonies. On these 

 rocky coasts, as elsewhere, any general degree of safety which might be 

 supposed to result from solid built bottoms and heavy structures, may be 

 far more than compensated by lightness of draft and tenacity of structure, 

 and facility of movement ; while in security against attack from a superior 

 steam force, the heavy built steam vessels could maintain no equality with 

 the light footed classes. The coast of Maine alfords all necessary shelter 

 and resources for this service ; and this description of force, if matured by 

 timely preparation, and put forth in our strength, might geuerally command 

 the coasts and shores, from Quebi'C to Nantucket. Two or three vessels 

 of the proposed class would doubtless prove more than a match for one of 

 the heaviest English steam ships ; and, for reasons already noted, the latter 

 might Uiid it ditlicult to escape. 



By proper arrangements, and, if needful, with the associated aid of one 

 of the ateam frigates, these lighter built steamers may be sent to any part 

 irf'the world, where their services may be desired, and where frienjly or 

 neutral ports can be found to afl'ord the necessary shelter and supplies of 

 fuel. Their great speed and efficiency might thus be employed with great 

 effect on an enemy's commerce and resources. 



I have been led, by the request of the commissioners, thus to explain, to 

 some extent, my views on this essential branch of public defence, and to 

 urge the adoption of a class of measures ou which I consider the fuiure 

 safety of the country may largely depend ; being fully persuaded that it is 

 not so much ou the magHitude,a.A oa the available quuUties u! ouf uavni 

 force, that we must rely for success in any future conflict with the great 

 mistress of the seas. 



cylinder at a pressure of 43 lb. to the inch, and "cut off" at one fonrleenth 

 of the stroke. As I could find no table showing the elfect of the expan- 

 sion of steam when carried so far, I prepared the following: — 



• I consider tlie Gladiator as being the proper type of the class D; except I 

 stlgblly debcieut in tengtti, whiclt would be belter at 200 feet. 



being 



EXPANSION OF STEAM. 



Obseritttions on the effect af using Steam expansivehj under different pres- 

 sures, and U'Aoi cut (iff' at different points. Reported in the American 

 •Journal of the Franklin Institute. 



I was led to the following calculations respecting steam, by a notice 

 published some time since iu the Franklin Journal, of the operation of the 

 Cornish Engines. The writer of tliat notice intimates, that the "duty," 

 said to be performed by the engines, is greater than the calculated power, 

 to be derived from the fuel, and that a new theory has been proposed to 

 account for it, by the ''momeutum" of the percussion of the steam upon 

 the piston. He states that iu some of the engines the steam is let into the 



From the above table it appears that one per cent, of a cylinder full of 

 steam, if suflTered to expand, will give an average pressure throughout the 

 cylinder equal to 5-0 per cent, of the pressure it exerted when entering the 

 cylinder; or that the same quantity of steam, if suffered to expand to 100 

 times its volume, will do 5-0 times as much work as if used, without ex- 

 pansion, through the whole stroke of the cylinder. And when cut off at 

 I'j of the stroke, as in the Cornish engines, the average pressure will be 

 more than one fourth of what it would have been, if fourteen times as 

 much steam of the same pressure had been used. This sufficiently ex- 

 plains the cause of the superiority of the "duly" performed by the Cornish 

 engines over those in which expansion is not carried to so great au extent ; 

 for it requires less water to be raised inlo steam to work expansively than 

 would be required to work with steam of the same average pressure, 

 and full cylinders. In the case of the Cornish engine the steam was used 

 at 45 lb. pressure for ,', of the stroke, giving au average pressure, agree- 

 ably to the table, of -259219 X 45 lb. = 11 005 lb., and to perform the 

 same work, with the full stroke, would have required steam of at least 

 this average pressure. Now to determine the quantity of water required. 

 Dalton says that steam obeys the same law as the gases with respect to 

 pressure, and theij have expansive force iu the raiio in which tliey are 

 compressed. Then steam of double pressure should coutain a double 

 quantity of water. The published tables of the specific gi-avities of steam 

 give an addition of weight of only about 87 per cent, to steam of double 

 pressure, wliich would contradict Dalton's position. Supposing, however, 

 that Dalton's law is correct, and that atmospheric steam contains 253 

 grains of water to the cubic foot, then steam having the above pressure of 

 11-005 lb. would coutain 433 grains; and steam of 45 lb. pressure would 

 contain 1012 grains of water per cubic foot. But, with this last, it requires 

 but,'j of the quantity, or {'W' zz) 72 grains to give the same average power, 

 when used expansively, as the 435 grains on the full cylinder plan. The 

 fuel required should be in proportiou to the water to be evaporated. 

 Watts's experiment with the open and closed boiler, each subjected fur an 

 equal time to aa equal heat, showed that the same quantity of water had 

 escaped, in steam, from the open boiler, as flew off from the close one, 

 upm opening the valve at the end of the operation ; thus proving that 

 equal weights of Water require equal quantities of heat to raise them into 

 steam, irrespective of pressure. On this principle, then, the Corn:sh en- 

 gine should require but ^'jj or about J of the fuel that would have been 

 required to work them ou full steam, which very nearly corresponds with 

 the " tluty" performed by the present Coruish engines compared with that 

 done by the engines formerly constructed by Bolton and Watt in the same 

 locality. 



Another principle comes iu play, in working expansively, which is lost 

 sight of when working with equal steam throughout the stroke— viz., that 

 matter in motion would never cease to move unless retarded by external 

 causes, and would require, to stop it, a power equal to its weight multi- 

 plied by its velocity. Now, iu working expansively, the steam is applied 

 at a pressure sufficient to start the load at a certain velocity, to continue 

 which. It is only necessary that the additional quantities of power should 

 equal the retarding forces of gravity, friction, and resistance uf air, until 

 the commencement of the next stroke. Now, in the Cornish engine, where 

 the steam is cut of at ^', of the stroke, the increments of power beyond 

 that point, or that portiuu of the power gained by expansion, amount to 

 nearly 2-04 times the direct power of the steam applied, and which gave 

 original velocity. This velocity must therefore be continued until the gra- 

 vity, friction, and resistance of air, amount to 2 04 times the original 

 power, applied before cutting off the steam. The whole weight of the 

 machinery and load thus operates, ou the fly-wheel principle, to continue 

 the motion, as the velocity given to them forms one of the factors of 



