26. To how many frequencies is the harmonic system usually limited?

27. What can you say about the commercial success of the step-by-step
method?

28. State the principles of a lock-out party line.

29. For what purpose is a condenser placed in the receiver circuit of
each station in the K.B. lock-out system?

30. How are the selecting relays in Roberts line restored to their
normal position after a conversation is finished?

31. What are the objections against the Roberts system?

REVIEW QUESTIONS

ON THE SUBJECT OF TELEPHONY

PAGES 287--315

* * * * *

1. What are electrical hazards?

2. When is the lightning hazard least?

3. What actions can electricity produce? Which involves the greater
hazard to the value of property?

4. When is a piece of apparatus called "self-protecting"?

5. Why must a protector for telephone apparatus work more quickly for
a large current than for a small one?

6. State the general problem which heating hazards present with
relation to telephone apparatus.

7. What is the most nearly universal electrical hazard?

8. Sketch and describe the saw-tooth lightning arrester.

9. Make diagram of the carbon-block arrester and state its advantages.

10. Describe a vacuum arrester.

11. Explain the reason for placing an impedance in connection with the
lightning arrester.

12. What is the purpose of the globule of low-melting alloy in the
Western Electric Company's arrester?

13. Why are not fuses good lightning arresters?

14. What is the proper function of a fuse?

15. Make sketch of a mica slip fuse.

16. Define _sneak currents_.

17. Make a diagram of a sneak-current arrester and describe its
principles and working.

18. Describe a heat coil.

19. Sketch a complete line protection.

20. Where is the proper position of the fuse?

21. Which wires are considered exposed and which unexposed?

22. Why is it not necessary to install sneak-current arresters in
central-battery subscribers' stations?

23. Sketch and describe the action of a combined sneak-current and
air-gap arrester, as widely used by Bell companies.

24. Describe the self-soldering heat-coil arrester.

25. What is the purpose of ribbon fuses?

26. What is a drainage coil?

REVIEW QUESTIONS

ON THE SUBJECT OF TELEPHONY

PAGES 317--386

* * * * *

1. What is a central office?

2. What are (_a_) subscriber's l