42 
THE TELEGRAPH 
taking the two pegs of Nos. 5 and 9 he thrusts them in on 
the same horizontal line, the first one for example. From that 
moment, 5 and 9 converse together, and the central office has 
no communication with them. Observe that the signals of 
Nos. 5 and 9 are removed from the call frame, and that as 
speech is not sufficient to set them in action, they remain so 
long as only speech is carried on. But when Nos. 5 and 9 
have done, each blows into his instrument and their signals 
re-appear, which shov r s the clerk that their lines are no longer 
required. He takes out the pegs and sets them again in the line 
“ terre ,” and the operation is at an end. 
It will be seen why the commutator has across all its 
vertical lines several horizontal lines. Suppose, for instance, 
that during the conversation between 5 and 9, 3 and 7 also 
wish to converse together. The pegs of Nos. 5 and 9 are in 
the first horizontal line, and if those of 3 and 7 w r ere also put 
there, the four telephones would be united and endless con¬ 
fusion would be the result. But by placing 3 and 7 on 
another line, as for instance on the second, this inconvenience 
would be obviated. No mistake can be made, as each line with 
a peg in it is engaged. 
All this description supposes that the correspondents belong 
to the same group. If they do not, the operation, although a 
little more complicated, is yet similar. Let us suppose that 
subscriber 5 calls and says that he wishes to speak with 
No. 83. The clerk has not this number in his group, A, 
which goes only as far as No. 30 ; the second group, b, ends 
with No. 60. It is therefore to the third group, c, that the 
required number belongs. The clerk of the first group 
answers that he is going to cause No. 83 to be called ; then he 
chooses a free line amongst the horizontal lines of his com¬ 
municator placed near the bottom. These lines are not shown 
in our figure, but their position is between the lines marked 
respectively d and tel. In the line so chosen, which we shall 
suppose to be marked “ 6,” he places the peg. He then w r rites 
this memorandum for the clerk attached to group c : Sub¬ 
scriber No. 5, group A, line 6, wishes to speak to subscriber No. 
83, group c. The clerk attached to the c group, on receiving 
this speaks to No. 83, and after receiving his reply places his 
peg on the horizontal band 6, and then he sends the memo- 
