Page:Popular Science Monthly Volume 14.djvu/562

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546
THE POPULAR SCIENCE MONTHLY.

reversal of her screw, the rudder produces none of its usual effects to turn the ship. In fact, under these circumstances, the effect of the rudder is to turn the ship in the opposite direction from that in which she would turn if the screw were driving her ahead. A ship with screw reversed requires, in order to turn a circle, double the radius of that required while steaming ahead; and, if it is difficult to govern her direction, it is more difficult to predict what that direction will be. When moving at full speed a screw-steamer requires five lengths more or less in which to stop herself, whereas by using her rudder and steaming on at full speed ahead she would be able to turn herself through a quadrant without having advanced five lengths in her original direction. Moral: When collision is imminent, steam ahead and be quick with the rudder. But, owing to the imperfection of the steering-apparatus now generally employed, quickness is impossible, and it takes a long time to put a large angle on the rudder. "The result is" (so say the Committee) "that it is often one or two minutes after the order is heard by the men at the wheel before there is any large angle on the rudder, and of course, under these circumstances, it is absurd to talk of making use of the turning qualities of a ship in case of emergency. The power available to turn the rudder should be proportional to the tonnage of the vessel, and there is no mechanical reason why the rudder of the largest vessel should not be brought hard over in less than fifteen seconds from the time the order is given. Had those in charge of steamships efficient control over their rudders, it is probable that much less would be heard of the reversing of the engines in cases of imminent danger." Clearly this is a question which calls imperatively for regulation by the Admiralty or some other competent authority.

 

The Candle-Fish.—The eulachon, or candle-fish (Thaleichthys pacificus), an inhabitant of the Pacific Ocean in the vicinity of British Columbia and northward, is worthy of a place among the curiosities of the animal kingdom. It is a small fish—about fourteen inches in length—and in appearance resembles a smelt. It is the fattest of all known fishes; and, in fact, the Indians use it, in the dried state, as a candle. On touching the tail to the fire it burns with a bright flame till the whole is consumed; more usually, however, a wick of woody fiber is passed through the body of the fish from end to end to insure continuous combustion. But the candle-fish is also employed as an article of food, and in spite of its fatness—indeed, on account of its fatness—is highly esteemed by the Indians as a warming food for winter. For this purpose they are dried and smoked in the spring, and then packed away. So preserved they are eaten whole, or the oil is tried out and eaten as butter. The take is usually very large, and only a small portion is dried and smoked. The remainder are piled in heaps till partial decomposition has set in; they are then packed in large boxes and the oil pressed out. This oil also is used as food, and it is said to be not altogether intolerable to the stomach of civilized man. The appearance of the first shoal of candle-fish in March is greeted by the Indians with extravagant demonstrations of joy. It is their Easter.

 

The Storage and Purification of Water.—In one of a series of papers on "Water-Supply for Small Towns," now publishing in "The Plumber and Sanitary Engineer," Mr. E. S. Philbrick has some remarks on the best material for constructing cisterns. He gives the preference to brick, as being sufficiently durable, and at the same time cheap. As brickwork is not adapted to resist tensile strains, brick cisterns, if of any considerable size, can not withstand water-pressure, by the strength of walls alone. So we put them underground, getting the earth-pressure from without to balance the water-pressure from within, and at the same time protect them from frost. The circular form generally used is strong enough in itself to resist the earth-pressure when the tank is empty, for this is a compressive force. The extended application of hydraulic cement thus enables us to construct, in almost any part of the world where commercial relations exist, an imperishable and incorruptible water-tank, so far as its own materials go.

But cistern-water will always be more or less contaminated by the accumulation of dust swept down from the roof. Hence a cistern should be thoroughly cleaned from