9. In what ways is an automobile engine like the gasoline engine and the electric motor used in rural homes for operating household machinery?
10. What is the shape of the knives on a lawn mower that makes it cut the same as a pair of scissors?
11. What may be the reasons for scissors not cutting as they should?
12. What are the essential features of a good incubator?
13. What is a thermostat? How does it work? Are thermostats of any use to the housewife on any other device than the incubator?
14. What mechanical factors are embodied in a typewriter? Find the pulley, the levers, the springs, etc.
15. What are the differences in a hectograph, a mimeograph and multigraph?
PART X