xxxiiia] EXCURSIONS AND EXAMINATIONS 413 



(6) The depth of the ocean is determined by fixing a piece of rope to 

 a heavy piece of metal which is lowered into the water, and as soon 

 as it touches the bottom the weight is no longer felt and the rope is cut 

 off at the surface of the water ; the rope is then measured. It is brought 

 up by a diver. 



(7) The depth of the ocean is determined by sounding or pianoforte 

 wire which is let down until it reaches the bottom of the ocean ; great 

 care must be taken to catch the sound. 



Equally gross ignorance is shown as to the mariner's com- 

 pass, the question being whether it always points due north ; 

 if not, why not ? 



(1) The mariner's compass do not always point due north because if 

 it did on board a ship, the captain of the ship would want to go south and 

 it would guide him the wrong way, instead of south it would guide him 

 north, so it is made to turn N.S.E.W. The mariner's compass is made 

 to turn round in any way in which the captain wishes to turn it, so as to 

 guide him which way he wants to go. If he wants to go to the south he 

 puts the point to the south, etc. They are used by men who want to go to 

 different parts of the world. Say if a man is lost in travelling to Germany 

 he looks at his compass, and if it is north he puts the point north, or 

 if it is south, etc. 



(2) The mariner's compass does not point due north because the wind 

 affects it. If the wind is blowing hard the dial points slightly to the 

 north, and when it is a heavy storm the dial points nowhere, but just 

 swings backwards and forwards. 



Another subject of the greatest interest and one that can 

 be very easily taught to even young children by a number of 

 simple and easy experiments, is that of the weight and 

 density of the atmosphere, and the construction of the 

 barometer. Some knowledge of these subjects is essential to 

 a clear understanding of a great number of natural phe- 

 nomena. Yet this is how, so late as 1889, some of these 

 students replied to easy questions about it : — 



(1) The weight of the air can be determined by the law of gravitation. 

 For example, take an apple from a tree and let it go. What happens ? 

 It falls to the ground. This shows that the air is heavier and attracts 

 the apple at the ground. Therefore we can say the apple does not fall, 

 but it is the ground that attracts it. By that process we could discover 

 or determine the weight of the air. We are able to move about because 

 the earth attracts us, and so we are able to move about in this dense 

 mass of air under us. 



