8 THE SCIENTIFIC PAPERS OF 



towards the end of each stroke, against projecting lugs of a lever 

 below, which, by the slight motion imparted to it, alternately 

 broke and restored the circuit, exactly as the valve-lever of a 

 steam-engine alternately admitted and discharged the steam. The 

 circuit of the line wire was not completed, until both or all the 

 communicating instruments had accomplished their return 

 stroke, and, until then, no fresh motion could take place. 



In depressing a key of any one instrument, a projecting lever 

 on the ratchet-wheel was stopped opposite the same ; the oscillating 

 lever was thereby arrested about half way in its return stroke, and 

 was, consequently, prevented from re-establishing the circuit. 

 The pointers on all the instruments stopped at that moment 

 opposite the same letter of the alphabet, and could only resume 

 their motion after the depressed key was released. The internal 

 arrangement of the printing instrument was the same as that of 

 the indicating instruments, with this exception, that instead of the 

 pointer upon the rotating spindle, there was a disc of thin steel 

 plate, divided into thirty segments, upon the extremities of which 

 types representing the letters of the alphabet were soldered. 



The instrument contained a second electro-magnet, of com- 

 paratively large dimensions, through the coils of which a local 

 battery current passed, each time the working lever of the in- 

 strument made an oscillation ; but it had no effect, because the 

 duration of each successive current was insufficient to effect its 

 massive armature. On stopping the instrument (by the depression 

 of a key), the local current of the large magnet continued and caused 

 it to attract its armature. This caused a hammer to strike with 

 considerable force under a letter of the type-wheel, corresponding 

 with the letter on the depressed key, which was forced upwards 

 against an inked cylinder and paper through the breadth of one 

 letter by a ratchet motion, thereby fitting it for the reception of 

 another impression. The alarums were worked on a similar 

 principle. 



It had been a matter of surprise how it was possible to produce 

 such powerful effects by galvanic action, without the aid of 

 clockwork, &c., seeing that under ordinary circumstances it hardly 

 sufficed to release a detent, or to deflect a needle. The advantage of 

 the principle of self-interception of current was here made apparent, 

 ft enabled them to include the batteries at the various stations 



