THE PEOGRESS IN STEAM NAVIGATION. 581 



differences lie in the requirements for passenger accommodation as 

 compared with the requirements for armament of the torpedo vessel. 

 No one has yet proposed to extend the torp(>do vessel s^^stem to sea- 

 going ships of large dimensions. Very similar conditions for the pro- 

 pelling apparatus have been accepted in a f(>w cruisers of considei-ahle 

 dimensions, Avherein high speeds for short periods were required. It 

 is, however, unquestionable that in many ways, and particularly in 

 regard to machinery design, the construction of torpedo vessels has 

 greatly influenced that of larger ships. 



One important consideration must not })e overlooked. For short- 

 distance steaming at high speeds economy in coal consumption is of 

 little practical importance, and it is all important to secure lightness 

 of propelling apparatus in relation to power. For long-distance 

 steaming, on the contrary, econcmiy in coal consuinptioii is of primaiy 

 importance, and savings in weight of propelling apparatus, even of 

 considerable amount, may be undesirable if they involve increased coal 

 consumption. Difi^'erences of opinion prevail as to the real economy 

 of fuel obtainable with boilers and engines such as are fitted to torpedo 

 vessels. Claims are made for some vessels which represent remarka- 

 ble economy. Only enlarged experience can settle these (questions. 

 Endurance is also an important quality in seagoing ships of large size, 

 notmerel}^ in structure, but in propel ling apparatus. Theextreme light- 

 ness essential in torpedo vessels obviously does not favor endurance, 

 if high powers are frequently or continuousl}^ required. Still it can 

 not be denied that the results obtained in torpedo vessels show such a 

 wide departure from those usual in seagoing ships as to suggest the 

 possibility of some intermediate type of propelling apparatus ai)i)lica- 

 ble to large seagoing ships, and securing sufficient dural)ility and 

 economy of fuel in association with further savings of weight. 



THE PARSONS TURBO iilOTOR. 



The steam tur))o motor, introduced by Mr. Charles Parsons, with its 

 very high rate of revolution, reduces the weights of machinery, shaft- 

 ing, and propellers greatly below the weight required in the qui<k(>st 

 running engines of the reciprocating type. This reduction in the pro- 

 portion of weight to power carries with it. of course, th«' possibility of 

 higher speed in a vessel of given dimensions; and when large jx.wers 

 are emploved the absolute gain is very great. An illustration of this 

 has been given by Mr. Parsons in the r>n'h!»hi. That reinarkal.le 

 vessel is 100 feet long and of 44i tons displacrnient, l.ut she has 

 attained 33 to 34 knots in short runs. There are three shafts, each 

 carrving three screw propellers, each shaft driven by a steam turbme 

 making over 2,000 revolutions at full speed, wlien an aggregat.> of 

 more than 2,000 horsepower is developed. A water-tube boihr of 



