CtC WHfflS 



Fig. 20. 



STEAM NAVIGATION. 



CHAPTER IV. 



68. Effect of the screw-propeller reaction on the vessel. 69. Their best 

 practical proportion . 70. Their varying pitch . 71. Relative advantages 

 of screw and paddle-wheels. 72. Their effects in long sea-voyages. 

 73. Experiments with the "Rattler" and " Alecto." 74. These 

 experiments continued. 75. Admiralty experiments. 76. Govern- 

 ment report. 77. Application of the screw in the commercial marine. 

 78. Application of screw to mail-vessels. 79. Geared and direct 

 action. 80. Geared-eugines. 81. Fairbairn's internal gearing. 82. 

 Subdivision of the power among several cylinders. 83. Protection 

 from shot. 84. Regulation of slides. 85. Relative speed of screw and 

 vessel. 86. Engines of the "Great Britain." 87. Engines of the 

 "Arrogant" and "Encounter." 88. Various forms of screw-engines. 

 89. Cross action of H. M.'s screw steam-packet "Plumper." 

 90. Auxiliary steam-power. 91. Effect of screw-vessels head to 

 wind. 92. Nominal and real horse-power. 93. Official tables of the 

 strength of the steam-navy. 



68. THE screw, whatever be its form or structure, in driving 

 the water sternwards, sustains a corresponding reaction which takes 

 effect upon the screw-shaft, and produces an equivalent pressure 

 on its bearing to its anterior extremity. The force of this forward 

 thrust of the screw-shaft, combined with its velocity of rotation, 

 produced, in the earlier screw-vessels, considerable inconvenience 

 in consequence of the friction attending it, and several cases 

 LAKDNER'S MUSEUM OF SCIENCE. M 161 



Np. 128. 



