ACOUSTIC TELEGRAPHY. 
39 
which has been adopted by the Compagnie Generate des Tele¬ 
phones. In the first place the subscribers are divided into 
groups of not more than thirty each, and those who are most 
frequently in communication with each other are arranged to 
belong to the same group. To each of the groups a special 
clerk is appointed. This arrangement is obviously an advantage, 
though it may appear to entail some cost. The American 
systems have switchmen , who attend to many lines: a plan 
which is no doubt more economical, bub, on the other hand, 
increases the liability of mistakes being made. 
The clerk in charge of each group has in front of him a 
system of Swiss commutator like that represented in Fig. 12, 
