588 THK PKOGKESS IN STEAM N AVKiATlON. 



type of water-tul)e boiler in association with the high steam pressures 

 now in use. Greater safety, quicker steam raisin^;, and other advan- 

 tages, as well as economy of weight, can thus be secured. Some types 

 of water-tube boilers would give gi'eatei- saving in weight than the 

 particular type used in the foregoing comparison with cylindrical 

 boilers. Differences of opinion prevail also as to the upper limit of 

 steam pressure which can with advantage be used, taking into account 

 all the conditions in both engines and boilers. From the nature of 

 the case, increases in pressure beyond the UJO pounds to 180 pounds 

 per square inch commonly reached with cylindrical boilers can not 

 have anything like the same effect upon economy of fuel as the corre- 

 sponding increases have had, starting from a lower pressure. Some 

 authorities do not favor any excess above 250 pounds per square inch 

 on the l)oilers. Others would go as high as .Soo pounds, and some still 

 higher. 



Passing to the engine rooms, the use of higher steam pressures and 

 greatei- rates of revolution may. and ])i-obabJy will, produce reduc- 

 tions in weight compared with power. Tlie use of stronger materials, 

 improved designs, better balance of the moving parts, and close 

 attention to details have tendi'd in the same direction without sacrifice 

 of strenuth. Necessarilv there nnist be a sufficient margin to secure 

 both strength and endui'ance in the motive power of steamships. 

 Existing ai"i"angements are the outgrowth of large experience, and 

 new de])artures must be carefully scrutinized. The use of rotary 

 engines, of which Mr. Parsons's turl)o-motor is the leading example at 

 present, gives the prospect of still fui'thei" economies of weight. Mr. 

 Parsons is disposed to think that he could al)out halve the weights 

 now required for the engines, shafting, and ])ropellers of an Atlantic 

 liner, while securing pro]ier strength and duraltility. Tf this could be 

 done in association with the use of water-tu))e boilers it would effect a 

 revolution in the design of this class of vessel, permitting higher 

 speeds to be reached without exceeding the dimensions of existing 

 ships. It does not appear prolmble that, with coal as the fuel, water- 

 tube boilers will surpass in economy the cylindrical boilers now in use; 

 and skilled stoking seems essential if water-tube boilers are to be equal 

 to the other type in rate of coal consumption. The general principle 

 holds good that as more perfect mechanical appliances are introduced, 

 so more skilled and disciplined management is required in order that 

 the full benefits may be obtained. In all steamship performance the 

 '"human factor" is of great importance, but its importance increases 

 as the appliances become more complex. In engine rooms the fact has 

 been recognized and the want met. There is no reason why it should 

 not be similarly dealt with in the boiler rooms. 



Liquid fuel is already substituted for coal in many steamships. 

 When suflacient quantities can be obtained, it has man}^ obvious advan- 



