HISTORY AND PROGRESS* 49 



battery, and b with the zinc pole of the same, through the 

 spring s'. 



On the lower side of a, and on the upper side of b, are 

 attached projecting pieces of metal, i and *, which play 

 between the springs t t' and T T', respectively. When the 

 handle is vertical, the metal arms i and i' are also vertical, 

 and the springs t and t' repose against the opposite sides of 

 the rest k. On turning the handle to the right, however, 

 the spring t' is lifted by the projection i from the rest k, 

 and the projection i 1 makes contact with r, whilst t and r' 

 remain unmoved. The spring r is not seen in the figure. 

 The circuit is thereupon completed from the pole of the 

 battery, through N, spring s, half a of the arbor, the arm 

 *', spring r, terminal T, earth, and from the + pole of the 

 battery, terminal p, spring s', part b of arbor, arm i, spring 

 t', multiplier, terminal L, line, opposite station apparatus, and 

 earth. 



The opposite springs are lifted and the current reversed 

 on turning the handle the other way, The apparatus serves 

 both as transmitter and receiver. When receiving signals, 

 the handle remains vertical. The currents arriving by the 

 line pass through L, coils of the indicator, spring i 9 metal 

 stop k, spring t, terminal T, to earth, and the needle is 

 deflected to the right or left, according as the arriving 

 current is positive or negative. 



If signals are to be given by the apparatus, the manipu- 

 lator has only to turn the handle to the right or left to effect 

 corresponding deflections of the needle of his own instru- 

 ment and of that at the station to which he is sending. 



The code of signals for the letters of the alphabet, &c., is 

 engraved on the dial, either by means of arbitrary signals, 

 as in Fig. 23, where the right-hand deflections are shown by 

 the numeral 3 and left-hand by the numeral 1, or by means 

 of strokes of different lengths. In the latter case the long 

 and short strokes indicate the number and direction of the de- 

 flections representing each letter ; and shorter strokes are to be 

 executed before the longer ones to which they are attached. 

 The letter A, for example, is indicated by two deflections to 



