Report of the House of Commons on Steam- Boats. 123 



them * ; sometimes there is a vast excess, sometimes a defi- 

 ciency, and sometimes a total absence of the resisting medium. 

 " These irregularities throw the migovcrncd and almost irre- 

 sistible power of the steam-engine into those convulsive starts 

 that meet no other controlling check but the arm of the crank, 

 from which it vecoils with increased energy to the opposite 

 side, occasioning thereby those destructive sliocks, those alter- 

 nate strains and wrenchings, which a frequent recurrence must 

 render fatal to the cranks and to the shafts, besides other parts 

 of the machinery," To remedy these defects by such com- 

 binations of machinery as may enable the engine to adapt and 

 accommodate itself spontaneously to all the exigencies incident 

 to its peculiar service, is one of the chief objects which should 

 attract the attention of engineers. 



The great size of the boilers, as now made, is very disad- 

 vantageous. They occupy a very inconvenient portion of the 

 space within a vessel. 



The method of fixing *he paddles is a very defective part of 

 the machinery: the oblique action of them in entering and 

 departing from the watei-, produces that trenmlous jarring 

 which serves to loosen the seams and the bolting of the knees 

 and beams of the vessel ; it also occasions a very great loss of 

 the steaming power. 



In respect to the degree of strength proper to be given to 

 the machinery, almost all the engineers, who have been ex- 

 amined, concur in the opinion that it ought to be very consi- 

 deraljle. Messrs. Wood say, " All the connecting machinery 

 should be twice the strength for ordinary work on shore." 

 Mr. Donkin says, that every part of the engine should be made 

 at least of three times the strength, wliich, by estimation, 

 would be required for any force to which it might be exposed. 

 " Accidents," he observes, " are most likely to hajipen at a 

 time when the suspension of the power of die engine would be 

 most fatal." 



Wrought-iron is strongly recommended to be used in place 

 of cast-iron ; and though some of the witnesses have expressed 

 doubts of the jiracticabilily of making large shafts of wrought- 

 iron, Mr. Donkin docs not hesitate to say, that " they can al- 

 ways be got quite perfect, if a sufficient price is gi\en for 

 them." 



As so niudi of the safety of die vessel depends upon die 

 workmansliip of the materials, they should be proved before 

 tliey are used, by a pro])er proving engine iur trying Ujcir 

 strength, as well by a force acting in a twisting direction, as 

 by a strain in the direction of their Icnglli. 



* Mr. Hrunel's cviilcncc, pii. l7-'>, 17G. 



Q 2 Allien 



