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 ef- 

 fect 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-appa- 

 ratus 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 pow- 

 er 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 sec- 

 onds 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." Clear- 

 ly this is a question which calls imperative, 

 ly for regulation by the Admiralty or some 

 other competent authority. 



The Candle-Fisli. — The eulachon, or can- 

 dle-fish ( TJialeichthys pacificus), an inhabitant 

 of the Pacific Ocean in the vicinity of Brit- 

 ish 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 resem- 

 bles 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 de- 

 composition 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 demonstraticna 

 of joy. It is their Easter. 



Tlie Storage and Pnrififation 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. Philbrickhas 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 balauce the water-pressure 

 from within, and at the same time protect 

 them from frost. The circular form gener- 

 ally used is strong enough in itself to resist 

 the earth-pressure when the tank is empty, 

 for this is a compressive force. The ex- 

 tended application of hydraulic cement thus 

 enables us to construct, in almost any part 

 of the world where commercial relations ex- 

 ist, 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 



