376 Recent Advances in Telegraphy, IJ u ly? 
spring and contadt-point a to the line. At each vibration of 
the reed the contact between the spring and a is made and 
broken, and the circuit opened and closed. Whenever the 
signalling-key is depressed, therefore, an intermittent current 
enters the line. 
Mr. Gray also procures the intermittent current by means 
of a vibrating bar or string, as in Fig. 14, where A is a thin 
steel bar stretched by the screw s, and carried by a fixed 
metal bar or frame, b. The bar A vibrates between upper 
and lower contadt-points, c, d. mm are two eledtro-magnets 
whose poles are let through the bar B, so as to adt upon the 
vibrating bar. p p are pillars supporting the whole. In 
this arrangement a local battery is also employed to set and 
maintain A in vibration : this is done, however, in the a dt 
of signalling. On closing the signalling-key the local cur- 
rent passes to the upper contadt c, against which the bar A 
rests. From thence it passes, by means of the bar b and 
wire w, through the magnets M M, completing its circuit. 
These magnets then attradt the bar downwards in its 
middle, plucking it away from contadt with c, and bringing 
it into contadt with d underneath. The local circuit being 
thus broken, however, the bar springs back again into con- 
tadt with c, to be plucked down again as before. In this 
way the bar is started vibrating. The line circuit is made 
through the lower contadt d , the bars B and A, and the 
pillar p. At every vibration of the steel bar A it is inter- 
rupted, and an intermittent current set up in the line. 
In both of these methods the number of intermissions in 
the line current will correspond with the number of vibra- 
tions of the vibrators. By employing in the first method 
reeds of different pitch, and in the last bars or strings of 
different dimensions and tension, distindt intermittent cur- 
rents will be produced. 
The principal receivers for interpreting these currents into 
distindt audible sounds are represented in Figs. 15 and 16. 
In Fig. 15 M is a double eledtro-magnet supported over a 
resonance pipe closed at one end. The soft-iron armature 
of the eledtro-magnet, t T, is rigidly fixed to one pole at t , 
the other end being free to vibrate in front of the other pole 
at T. When the intermittent current from the line passes 
through the eledtro-magnet the free end of the armature or 
tongue is set into corresponding vibration, and the air- 
column in the resonance box, vibrating in unison with it, 
gives out an audible note. It is easy to see how, by em- 
ploying a number of separate transmitters, such as described, 
to superimpose separate intermissions in the line current, 
