534 THE POPULAR SCIENCE MONTHLY. 



of only eleven tons, boiler, water, engine, condenser, propeller, and 

 shaft included. 



The special feature of the boat is the enormous power developed per 

 hundredweight of propelling machin'ery. The boilers evaporate eight- 

 een pounds of water per hour per square foot of heating surface, and 

 120 pounds of coal per square foot of grate-surface. This is fully six 

 times the amount of water and coal usually dealt with per square foot 

 of surface in furnace and boiler. Such a forced combustion precludes 

 all thought of economy, yet a one horse-power is secured at full speed 

 with an expenditure of three and a half pounds of coal. The forced 

 draught is secured by maintaining in the stoke-hole an air-pressure cor- 

 responding to a column of water six inches high ; this renders the 

 stoke-hole quite cool and comfortable. 



One ton of coal will last for a run of 100 miles at a ten-knot speed. 

 A speed of twenty-two and a half knots has been secured in trials last- 

 ing three hours. This is a speed of 2,250 feet a minute, or thirty- 

 seven and a half feet a second, and seems almost incredible. 



But, remarkable and important as these results are in the phase of 

 steam-engineering, these little vessels have revealed in their perform- 

 ances under speed-trials facts of equal importance to another depart- 

 ment. The speeds attained are high even for large steam- vessels, but 

 enormously high for such small vessels. It is found that passing the 

 ten and twelve knot point, which bears about the same ratio to these 

 little boats that eighteen knots an hour does to large steamers, the 

 ratio of resistance to the speed decreases, and at the fifteen-knot point 

 it is about the 3|^-power, at the eighteen-knot point about the 3-power, 

 and sometimes at the twenty-two-knot point is as low as the 1^-power 

 of the speed. 



Effort has been frequently made to utilize steam at much higher 

 pressures than I have mentioned, but, owing to the solvent nature of 

 steam or water at a high temperature, the results have not been satis- 

 factory ; among many difficulties encountered was that of lubricating 

 the cylinders. 



Loftus Perkins, an English engine-builder of prominence, is devot- 

 ing much time to the use of steam at about five hundred pounds press- 

 ure, and with some success. Unfortunately, the gain to be anticipated 

 from the use of these exceedingly high pressures does not seem to be 

 very great on trial. The Anthracite, a small steamer fitted with en- 

 gines and boilers specially adapted to the utilization of steam at five 

 hundred pounds pressure, was more wasteful than many steamers using 

 steam at one hundred pounds. However, here is a wide field and one 

 that promises well. . 



Should the same change of law as to the resistance increasing as 

 the square of the speed be found to hold good in large steamers as in 

 the little torpedo-boats, we shall most of us live to see locomotive 

 speed's at sea. There is now building in this country an engine which 



