5 r >2 THE APPLICATJONS OF PHYSICAL FORCES. [BOOK v. 



if it is the right hand commutator whose spring has been placed 

 on the tongue m f . 



To sum up, if a motion of rotation is given to the handle of the 

 manipulator, so as to make it perform a complete revolution, there will 

 have been thirteen passages of the current through the line wire, and 

 thirteen alternate interruptions of it. Suppose we wish to send the 

 word " Paris," that is to employ the five letters P, A, E, I, s. After a 

 warning to the description of which we will return the sender turns 

 the handle from the cross to the letter p and leaves it for an instant in 

 the corresponding notch, and then continues the turning round to the 



FIG. 361. Indicator of Rreguet's dial telegraph, external view. 



cross. He stops at the letter A, and then passes to the letters \\, I, s, 

 in the same manner. 



Each time, that is for each turn, the number of sendings and 

 interruptions of the current is twenty-six, but there is a moment of 

 stoppage, corresponding to the moment when the handle stops at the 

 letter to be sent. These sendings and interruptions and stoppages are 

 reproduced in the same order at the receiving station, and it remains 

 to shew how they are indicated in the receiving apparatus of that 

 station, by making a needle move over the dial of that apparatus, and 

 reproduce identically the motions of the handle. 



