280 Introduction to the Study of Science 



as Pikes Peak, Colorado. Explain how this makes possible a high 

 tractive effort in proportion to the weight of the locomotive. Would 

 such locomotives be geared to move slowly or rapidly? Why? 



7. What evidence is there that rails are depressed as the wheels of 

 the train pass over them ? 



8. Mention several good illustrations of friction taken from a base- 

 ball game ; a football game. 



9. How has the use of the automobile influenced road building in 

 your vicinity? In the country at large? 



10. The United States Government gave the Union Pacific Rail- 

 road Company a large amount of land to encourage the construction 

 of the road. Justify this use of the public lands. 



11. Why are steel rails not made in the form of solid, rectangular 

 bars? 



V. BRIDGES 



118. Primitive and modern bridges. There are few roads 

 that do not need bridges. Highways and railways are making 

 increasing use of them in order to economize time and cost of 

 trackage and hauling. Not very many years ago a stream or 

 an abyss that could not be spanned by a felled tree or by a rope 

 used as a bridge, had to be forded, or crossed by a long, difficult 

 route. The log bridge and the swinging suspension bridge of 

 primitive construction shortened many roads, and also sug- 

 gested how man might make further use of his ingenuity in 

 overcoming such obstacles to rapid and easy travel. The 

 primitive bridge involved the principles which underlie modern 

 bridge engineering. To-day these principles are realized more 

 fully in such designs as give the greatest possible strength and 

 utility, and in construction with such materials as stone, con- 

 crete, and steel. The modern bridge is one of the finest ex- 

 amples of scientific and artistic engineering. It is a thing of 

 beauty as well as of utility. It is also an instance of the success 

 which men have achieved with the aid of scientific knowledge 

 in conquering some of the greatest obstacles to transportation 

 and travel. 



119. The principle of the girder. You may find in your 

 vicinity examples of the simple bridge with log or heavy timber 



