HISTORY AND PROGRESS. 63 



an escapement, so that when the armature is moved up and 

 down, the escapement, moved by it, works round a little 

 scape- wheel, e, carrying a light pointer, p, around the circum- 

 ference of a dial, D ; it is evident that when the apparatus is 

 connected by the wires as shown in the figure, the armature 

 will always be moving up and down, and the pointer, there- 

 fore, always running round the dial. 



If we now insert into the same circuit another electro- 

 magnet, E, with a similar armature, escapement, tooth- wheel, 

 and dial, the electro-magnets being both magnetised by the 

 same currents and demagnetised at the same time, the move- 

 ments of the armatures will be synchronous ; and if the 

 pointers have been started from the same places on each dial, 

 they will stop at the same points on the dials whenever the 

 armature E is arrested in its upward or downward motion. 



This apparatus is employed to a considerable extent on the 

 Prussian railway lines. It has, however, not found any ex- 

 tensive employment in England. Apart from its somewhat 

 complicated mechanism and costliness, it is undoubtedly the 

 nearest approach to perfection in a telegraph apparatus of 

 anything we have yet seen. 



50. House's Printing Telegraph. This telegraph, the work 

 of Mr. House, of New York, was the subject of an applica- 

 tion for patent in 1845. It belongs to the class of step-by- 

 step motion telegraphs, and consists of two separate parts : 

 the transmitter or commutator, and the receiver or printing 

 instrument. 



The transmitter is composed of a contact-wheel in every 

 way resembling that used by Wheatstone in one of the modi- 

 fications of his dial instrument, which, in turning, sends a 

 series of currents from a battery at the transmitting station. 

 As each make-and-break of the circuit indicates a letter, 

 whenever a letter is to be transmitted, the contact- wheel is 

 arrested at a certain point by which either the current is 

 allowed to flow, or is interrupted during the continuance 

 of the indication according as a contact-spring happens to 

 rest upon a tooth of the wheel or opposite a space, at the 

 moment of stopping. 



