HISTORY AND PROGRESS, 63 



the vertical shaft, the coils of the magnet, and line wire to 

 the other station, where it circulates in the coils of the 

 magnet, the vertical shaft, &c., and goes to earth. 



In traversing the coils of the magnets of both instruments, 

 the current weakens the attractions of the armatures to the 

 poles of the electro-magnets ; the former are forced off by 

 the spring, the screws d' are raised, and the levers L at the 

 same time depressed. The pallets h of the escapements h ti, 

 are thereupon released, the axes i put into gear with I, and 

 the type- wheels released. During the revolution made by 

 the axes *, the cylinders a are raised by the cams, and lift 

 the paper up to the printing-wheels at the moment when the 

 latter are unlocked. No letter is printed, because the blank 

 space in the type- wheel occurs just there. The paper strips 

 and cylinders descend again ; the former advancing a step. 

 The clicks are then disengaged from the ratchets, and the 

 pallets h recaught by the levers L', which were lifted up, 

 causing the armatures to be pushed down again to the poles 

 of the magnets. 



If a key answering to any letter be now pressed down, the 

 current is repeated the moment the chariot passes over the 

 raised contact pin ; the printing axis is put in motion, 

 the letter printed, and the paper pushed on as before, and so 

 on, until the message is completed. 



It sometimes happens that the apparatus do not agree 

 when one of the stations sends its message. In this case, 

 the employe at the receiving station advises his corre- 

 spondent of it by giving him a signal ; both then arrest their 

 type- wheels, and the transmission is recommenced, begin- 

 ning always with the blank. 



To avoid the inconvenience of irregular working, which 

 might arise from changes in the battery power, Professor 

 Hughes has adopted a method of short circuiting the coils 

 of the electro-magnet the instant after the armature is 

 released, that the current, whatever may be its intensity, 

 comes into play only long enough to effect the required 

 weakening of the magnetic attraction. This is done by con- 

 necting one end of the electro-magnet coils with D, and the 



