[25] U. S. FISH COMMISSION STEAMER ALBATROSS. 27 



POWER ABSORBED BY THE FRICTION OF THE WETTED SURFACES 

 OF THE HULL AGAINST THE WATER. 



Taking the resistance of the water to a square foot of smoothly- 

 painted surface of the hull, moving at a velocity of 10 feet per second, 

 to be 0.45 of a pound, and (according to the method of Chief Engineer 

 Isherwood, U. S. N.) deducing from the speed of the vessel the mean 

 speed of its immersed surfaces due to the inclination of the water-lines, 

 there results a speed of 16.35076 feet per second and a consequent sur- 

 face resistance of (10 2 : 0.45 : : 16.35076 2 : ) 1.203063 pounds per square 

 foot at that velocity. The aggregate wetted surface during the above- 

 mentioned voyage was 7350.44 square feet, and the powerexpended in this 



^7350.44x1.203063x16.35076x60 \ 0/>0 ono . 

 resistance was ( <n00( l = ) 262.893 horses; 



consequently, of the 289.642 horses-power required to propel the hull, 



/262.893xl00 \ on _ Q . 



V — 289 C4-9 — = ) 90-73 per cent was expended in overcoming the fric- 

 tion of the hull on the water, and the remaining 9.27 per cent was ex- 

 pended in displacing the water and overcoming the pressure of the 

 wind against the upper part of the hull, the spars, and the rigging. 



SVEDBERG GOVERNORS. 



In a heavy sea-way a ship, from excessive pitching, will sometimes 

 throw the screw out of water sufficiently to relieve it of the resistance 

 of the water ; at such times the screw and engine, thus released, will 

 spin around very rapidly, endangering the machinery. To prevent this 

 it was formerly the custom to station a man at the throttle who would 

 close that valve when the engine began to speed up (to "race"), and to 

 open the throttle when the engine slowed down. This operation was 

 never satisfactory, and gave birth to the invention of many marine 

 governors, the majority of which were centrifugal in principle, and con- 

 sequently depended on the speeding of the engine to close the throttle, 

 or, in other words, to slow the engine after the racing had commenced. 

 The object of the Svedberg governor is to anticipate the racing and to 

 close the throttle- valve before it commences. 



To accomplish this an air-chamber A, Plate XVIII, is placed at the 

 stern of the ship, as low down as it can be fixed ; the top of this air 

 chamber is connected to the top of a mercury-cup by a pipe; this mer- 

 cury-cup (B, Plate XVIII) is made on the principle of a Wolf jar, and 

 besides mercury it contains a wooden float on the lower end of the rod r, 

 which passes through the oblique cylinder d to the surface of the mer- 

 cury ; the cylinder, though in the same casting with the mercury-cup, 

 has its lower rim immersed in the mercury. Any elevation of the stern 

 of the ship, or any rise or fall of the water under the stern of the ship, 

 .will increase or diminish the pressure in the air-chamber A, which press- 

 ure is promptly communicated to the mercury-cup B, and depresses or 

 lifts the surface of the mercury in the cup ; but as the lower rim of the 



