SECT, x.] OF STEAM NAVIGATION. 315 



by 9-2 feet for each wheel, making an area of 36'8 feet for both, or the breadth of 

 the wheel 9-2 feet. 1 



The other proportions of the engines will be found by the general rule, (art. 415.) 

 except that a somewhat smaller quantity of water produces the steam, owing to its 

 being of a higher temperature, (see art. 90.) but it is only about 2 per cent less, 

 and the fuel required is not sensibly altered ; there is also a slight advantage by 

 the force of the steam being less in the condenser than when pure water is used. 

 (See table, art. 94.) Hence, the cistern of water to contain the condenser is 

 omitted without loss. The engines should be prepared to work expansively, to be 

 adjusted by hand, (see art. 419 and 481.) and the strength of the parts will be 

 found by art. 496 527 : the management of the water is treated of in art. 565. 

 and the parallel motion, art. 488 495. 



656. I think it would be desirable to try the effect of giving a considerable 

 degree of elasticity to the arms of the paddles, and to form the boards in the 

 manner shown in Fig. 28. page 305. The wheels of vessels appear to be kept too 

 forward, so as to keep the fore part of the vessel constantly heaving upwards ; and 

 such an action is unfavourable. A vessel should bear firmly in the direction of its 

 motion to move well ; and that this remark is true in practice as well as theory, 

 may be inferred from the fact, that in the present construction they find an 

 advantage in using the sails to steady, and determine the direction of the vessel's 

 motion. In vessels for towing, 2 this may be adopted with still greater advantage ; 

 and in both cases the proper place for the wheels appears to be behind the centre of 

 gravity of the vessel. 



The following Tables are collected chiefly from the evidence printed in the 

 Reports on the Holyhead Steam Packets, by the committee appointed by the 

 House of Commons ; and will afford a means of comparing the practice of different 

 manufacturers : 



1 The proportions of the vessel in this case are as nearly those of that called the James Watt, as I 

 could ascertain them ; and in the tables which follow, the best information I could procure 

 respecting that vessel is given in order to compare the calculated with the reported effect : the 

 velocity is that in still water, that is, the velocity in the river with that of the current deducted 

 therefrom. 



* The power required for towing a vessel may be estimated by art. 622. 



