282 SCIENCE OF HOME AND COMMUNITY 



gas, and the electric horn, operated by electricity. In the 

 electric horn a membrane is caused to vibrate by means of 

 a cam provided with many points and rotated by a motor. 



FIG. 1 10. -T- Shaft brake of band form. 



FIELD EXERCISE 6 



Purpose. To study the parts of an automobile and see how 

 it is run. 



Directions, i. Arrangements should be made with some 

 mechanic in a garage to have the class visit the shop when an 

 auto is being taken apart to be fixed. The uses of the various 

 parts can then be explained to the members of the class. 



2. Arrangements can also doubtless be made with some of 

 the parents of the members of the class who own an auto, to 

 take small groups on an auto ride and explain the method of 

 running the car. 



SUPPLEMENTARY QUESTIONS FOR CLASS DISCUSSION 



1. Name all the uses that you have seen made of automo- 

 biles. 



2. Which is more useful, the auto or electric trolley car? 



