164 



that's it ; 



mechanism. The handle, o, is in 

 this instance the crank, to which 

 the hand communicates motive 

 power : locomotive and marine 



a 



of its oblique fans, 7, upon the 

 water. It has recently been 



489. 



engines are contrivances in which 

 we apply a mighty steam arm to 

 the turning of an enormous crank, 

 by which motion is imparted to 

 machinery. 



6 i 



The propulsion of steam ves- 

 sels is now effected by means of 

 the Archimedean screw, 6 (so 

 called because it was first tried 

 }n connection with a vessel called 

 the J[rchimedes). The screw is 

 attached to the sternjceel, and 

 being made to turn rapidly, 

 propels the vessel by the action 



49t. 



proposed to place screw-propellers 



at the sides 

 of vessels, in- 

 stead of pad* 

 dle-whee Is. 

 It is thought 

 that by this 

 means vessels 

 will attain in- 

 creased speed, 

 as they will 

 be propelled sj 

 by two screws 

 instead ot one. 



In such case the cylinders, 8, 

 will have to be placed so as 

 to act upon wanks, 9, in the 

 axles of the screws, 10. 



The application of steam power to the propel- 

 ling of vessels, is one of the most important in- 

 ventions of modern times. By this application 

 of the steam-engine, man has so extended his 

 dominion over nature, that he may he almost 

 said to have completely overcome the wind and 

 the tide in traversing the deep. From the uni- 

 formity and amount of the power, the time of 

 transit upon rivers, and even the ocean, is not 

 only vastly different from the former modes of 

 navigating, but vessels may be calculated upon 

 in all weathers with as much certainty as can 

 well be desired. The advantages of steam navi- 

 gation have been immense, and are daily in- 

 creasing ; but it is at the same time worthy of 

 observation, that the advantages to mankind, 

 by its application to the art of war, are by no 

 means inconsiderable ; for, by diminishing the 

 chance of victory on either side, by uncertain 

 advantages of winds and currents, it increases 

 the probability of destruction, and lessens the 

 desire for battle. 



