66 BELL SYSTEM TECHNICAL JOURNAL 



Connections in North A merica 



Practically all the telephone stations in Canada have communica- 

 tion to the telephone stations in the United States. There are ap- 

 proximately 100 long distance circuits extending from cities in the 

 United States to important Canadian centers, including Halifax, 

 St. Johns, Montreal, Toronto, Hamilton, Winnipeg, Regina, Calgary 

 and Vancouver. The remaining cities are reached either directly 

 or by switching through the important centers. In addition to long 

 distance circuits there are, of course, many short distance circuits 

 connecting points on opposite sides of the boundary which have local 

 relations with each other. The various companies and provinces in 

 Canada cooperate very closely with the Bell Companies in the United 

 States in the maintenance of international service and, in general, 

 telephone practices are very similar or identical in the two countries. 



Telephone communication is extended from the United States to 

 Mexico by means of a telephone line crossing the border near Laredo, 

 Texas. Direct long distance circuits extend from points in the United 

 States to Mexico City, Tampico and Monterey and through these 

 centers to about one-half the telephone stations in Mexico. Local 

 toll circuits cross the border at a number of places. 



Telephone communication was established between the United 

 States and Cuba in 1921 by the placing of three telephone cables 

 between Key West and Havana. Each of these cables furnishes one 

 telephone circuit and a maximum of four telegraph circuits. The 

 requirements for the cables were exacting since a length of about 

 190 kilometers is combined with a depth of water having a maximum 

 of 1,860 meters. Each cable consists of a central conductor mag- 

 netically loaded with a wrapping of fine iron wire and insulated with 

 gutta percha compound. A metallic return path for the telephone 

 currents is furnished by heavy copper tape wrapped outside of the 

 insulation and, therefore, in contact with the surrounding water. 

 Three of the telegraph circuits in each cable are obtained by using 

 " carrier currents " at frequencies slightly above the voice range. The 

 fourth is obtained by using frequencies below the voice range. 



Connections to Europe 



In 1915 the Bell System experiments on radio reached the point 

 where telephone messages were transmitted by radio from the United 

 States and were successfully received by engineers sent for the purpose 

 to Paris and to the Hawaiian Islands. While the Great War delayed 

 technical and commercial development, in 1923 the Bell Companies 

 were able to carry out a successful demonstration of radiotelephone 



