28 REPORT OF COMMISSIONER OP FISH AND FISHERIES. [26] 



oblique cylinder d is immersed in the mercury, any rise in B will depress 

 the mercury in d, and will cause the float (and rod r) to fall or rise ac- 

 cordingly; and this rise or fall is directly proportional to the pressure 

 at the stern of the ship. The pressure exerted by the float is neces- 

 sarily small, while the power required to move the throttle-valve is 

 sometimes considerable, and for this reason a steam-engine is interposed, 

 the float moving the valve of the little engine, while the pressure of 

 steam in the little cylinder moves the throttle. In this engine the 

 piston and rod are fixed, while the cylinder moves upon the piston; 

 the valve chest and cylinder are cast in one, and the steam and exhaust 

 pipes slide through stuffing-boxes ; the cylinder is connected by the rod 

 e to the throttle-valve lever. The action of the machine is as follows : 

 The water, rolling from under the stern, causes a diminution of press- 

 ure in the air-chamber, which is transferred to the mercury-cup, lifts 

 the float and rod c, and, through the levers (shown in the engraving), 

 communicates a definite amount of motion to the valve; steam is thus 

 admitted to the cylinder and moves it to the right until the motion of the 

 cylinder has equaled that of the valve, when the ports are thus automat- 

 ically closed, and the cylinder and throttle- valve come to rest. By 

 changing the quantity of mercury in the cup, adjusting the length of 

 the rods or throw of the levers, the throttle- valve can be made to come 

 to rest at any desired position, or to work between desired limits. In 

 practice the machine works admirably, surpassing the writer's most 

 sanguine expectations. 



STEAM PUMPS. 



The Albatross is provided with three steam pumps, of the Davidson 

 pattern, as follows : 



Circulating pump, ISTo. 26. Light service. 



Boiler feed or fire pump, No. 5. Eegular. 



Hydrant pump, No. 5. Light service. 



The circulating pump has a steam cylinder 14 inches in diameter of 

 bore, a water cylinder 16 inches in diameter, and a stroke of piston of 

 14 inches. Its speed may be varied from 1 to 200 strokes per minute, 

 its ordinary speed being about 75 strokes per minute. It is piped to 

 pump from the sea or from th6 bilge, and to discharge into the con- 

 denser. Its maximum capacity is about 2,400 gallons of water per 

 minute. The writer has indicated the pump at several speeds, and con- 

 structed a curve (Fig. 1) in which the length of the ordinates refers to 

 the indicated horses-power and the abscissas to the interval between 

 speeds. The power of the pump can be ascertained at any moment by 

 counting the strokes per minute and referring to Fig. 1. The boiler 



