7-1 8 Home Nature-Study Course. 



we go slowly because we are obliged to; and the heavier the load the 

 slower we go. On the other hand, when we wish to run very swiftly we 

 drop the load so as not to be weighted down ; when college or high 

 school boys run races in athletic games they do not wear even their 

 ordinary clothing, but dress as lightly as possible in trunks and tights ; 

 they also train severely so that they do not have to carry any more flesh 

 on their bones than is necessary. How is it that in the case of a brook 

 just the opposite is true? The faster the brook runs the more it can 

 carry, and the heavier it becomes the faster it runs, and the faster it 

 runs the more work it can do. 



Facts for the Teacher. — It is well to impress upon the pupils that the brook is 

 a digger and carrier, these two things being the chief work done by the stream. 

 When it is not carrying anything, that is, when its waters are perfectly clear it 

 is doing the least work. The poets, as well as the common people, speak of the 

 playing of the waters of the brook when its waters are limpid and catch the sun 

 beams on their dimpling surface. In making the experiment to show how much 

 is carried by a quart of water taken from a roily brook, the children should be 

 questioned as to what makes water roily and should be made to understand that 

 the particles of soil are suspended in the water, thus giving it the roily color There 

 is likely to be very little sediment in the bottom of the jar from a single quart of 

 water, but the children should understand that there is a great amount of water 

 that is flowing past every moment and that there is, therefore, much soil being 

 carried by the whole brook. If the pupils study the banks of the brook they will 

 see that the current is cutting the banks where the soil is bare and that unless the 

 flood is very great indeed it does not cut banks which are covered by vegetation. 

 There are some easy experiments to show what the force of water can do when 

 turned against the soil. Pour water from a pitcher into any bed of soft soil and 

 see how quickly a hole will be made, and if the pitcher be held near the soil so 

 the current is not so strong less of a hole will be made than if the pitcher be held 

 high and the force of the water be thus greater. You can also observe in any 

 stream that where a swift current is being driven against a bank the latter is 

 undermined and even trees are thus toppled over into creeks and brooks. The 

 swift current, of course, digs away more earth at bends than when it is flowing 

 in a straight line; for ordinarilj^ when flowing straight the current is swiftest in 

 the bed of the stream and is, therefore, only digging at the bottom, but when it 

 flows around curves it is directed against the banks and, therefore, has much more 

 surface to work upon. It is thus that bends are cut deeper and deeper. If you 

 thrust your bare arm into the current of a flooded brook you will feel many bits 

 of gravel strike against it, and if you can reach to the bottom you will feel pebbles 

 being moved along over the brook bed. You should make the pupils understand 

 that these pieces of gravel enable the current to strike with an added force 

 comparable to the added power which a hammer or a pickaxe gives to a man when 

 he is digging in the earth. The current of a brook is always swiftest when its 

 waters are high, and as it can dig more and carry more when it is swift and high 

 it naturally is then doing its greatest work. The roar of a flooded stream is very 

 different from the murmur of its waters when they are low. 



