valves. This dirt may be arrested by a strainer (preferably a basket-strainer), but if the holes in the strainer be made very small, it will be constantly choking up. There should be at least two donkey-pumps on every steamer, and one should be a special clean-water pump, and the other a special bilge-pump. Both should be piped, as they are now, for all work, but not used for other work than that for which they are intended, except in emergencies. It is an unwritten law among engineers never to let the donkey feed-pump be used for any purpose except feeding the boilers or for fire purposes; and when it is known how easy it is to choke up a pump with bilge dirt, and also how embarrassing it is to an engineer to find the donkey feed-pump refuse to feed the boiler, we must respect that unwritten law. A careful engineer will always wash out his pump by pumping sea-water, after having pumped the bilge, and this should never be neglected. The Davidson Pump Company make their water-valve openings exceedingly large, and put in the kind of valves according to the duty required of the pump. One kind of valve is used for hot-water, another for cold (clean) water, and still another kind for bilge-water. All pump-builders use a brass lining, brass valve-seats, and brasscovered rods in the water-ends of pumps to be used for sea-water. The steam end of the improved pumps, such as the Davidson and the Worthington, are so perfectly made now that they can be throttled down to one stroke a minute, with a certainty of continuous running so long as the steam is supplied, and the steamthrown valves are so nicely adjusted that when the piston reaches the end of the stroke the steam-valve will then be "thrown" from one full opening to the other. With such perfect pumps, ordered for special purposes, the unwritten law must soon become a dead letter," and the steam-pumps used for washing decks and for all other purposes whereby labor can be saved. SPEED TRIALS. REMARKS ON THE TURNING OF SHIPS. PRACTICAL METHOD OF MEASURING A SHIP'S CIRCLE. WAVES. OBSERVATIONS OF THE DIMENSIONS AND PERIODS METHODS OF OBSERVING THE ROLLING AND DISPLACEMENT AND BUOYANCY. THE TONNAGE OF SHIPS. SAILING, ETC. CENTRES OF EFFORT AND LATERAL USEFUL RULES IN MENSURATION, ETC. INSTRUCTIONS FOR MASTERS AND SEAMEN IN LOCATION OF LIFE-SAVING STATIONS. INSTRUCTIONS FOR SAVING AND RESTORING ACCIDENTS, INJURIES, AND POISONS. WATER. FOREIGN SEA TERMS AND PHRASES. SPEED TRIALS. Measured Mile. To determine the true speed of a vessel when the runs are taken on the measured mile, half the number of runs being taken with the tide, and half against the tide. RULE.-Find the means of consecutive speeds continually found, until only one remains. * The ordinary mean of second means is generally taken as sufficiently accurate. Speed of the Current.-To find the speeds of the current in the line of the ship's course during her speed trials. RULE. Find the differences between the real speed of the ship, and her observed speeds on the mile during the several runs. Time and Knot Table. The minutes and seconds of time, in which a vessel passes over the measured mile, being known, the corresponding number of this table, will be the speed of the vessel in knots. Sec. 9 10 11 5m. 10m. 11m. 12m. 13m. 14m. 3m. 4m. |