LIST OF ILLUSTRATIONS. 
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Fig. Page 
1 Chappe’s Telegraph 8 
2 Signal Towers . . . . . . . • .11 
3 Mangin’s Military Telegraph (section).14 
4 Mangin’s Military Telegraph . . . . . • .15 
5 Leseurre’s Heliograph . . . . . . . . . 18 
5&Leseurre’s Heliograph (the screens) . . . . . .19 
6 Mance’s Heliograph . . . . . . . . . 20 
7 Telegraphic Communication ....... 29 
8 Gower’s Telephone.33 
9 Telephone Signalling Apparatus . . . . . .35 
10 Telephone Signalling Apparatus (diagram) . . . . . 37 
11 Box of Telephone Signals . . . . . . . .38 
12 Telephone Commutator. . . . . > . . . 39 
13 Telephone Exchange ......... 41 
14 Telephone Exchange . . . . . . . . . 43 
15 Telephone Switchman ........ 44 
16 Office Telephone .......... 45 
17 Telephone Employe Receiving a Call.46 
18 Despatch Carrier ...... .... 53 
19 Varley’s Valves.54 
20 Varley’s Valves.. . . . 55 
21 Varley’s Valves .......... 56 
22 Wilmot’s Valve.57 
23 Wilmot’s Valve ......... 57 
24 Siemens’ System of Tubes.61 
25 Diagram of Circuits.62 
26 Wells for Condensed Water.63 
27 Receiving and Transmitting Valves.64 
28 Receiving and Transmitting Valves . . . . . . 65 
29 Receiving and Transmitting Valves ..66 
30 Receiving and Transmitting Valves.67 
