XI. APPLICATIONS. 305 



encasing the coil in soft iron. The armature is shaped thus, 

 and is magnetised by induction from a compound bar magnet 

 placed behind. The crescent-shaped portion plays between the 

 inner ends of the casings, which for that purpose do not quite 

 meet, but leave the central portion of the coil exposed. 



An ordinary magnetic needle pivoted below the coil is acted upon by the 

 latter, and serves as an indicator to call attention. 



The armature is held up against knife-edge bearings by two helical springs, 

 and the adjustment is effected by varying the tension of one of them. 



1541. Belays used by the Electric Telegraph Company, 1356. 

 Later form of relay which superseded No. 38 ; a few are still 

 used by the Post Office. 



A horizontal bar of soft iron is pivoted vertically, and free to move in 

 the interior of two cylindrical bobbins. The ends of the bar which project 

 beyond the bobbins play between the poles of horsehoe permanent magnets 

 fixed at each end. The relay is adjusted by moving the stops, and conse- 

 quently the soft iron bar, to one side or the other. 



1542. Belay for Bright's Bell Instrument. 



A relay or repeater for relaying the signals of the Bright's Bell instrument 

 used on the long lines of the British and Irish Magnetic Telegraph Company, 

 when owing to leakage at the supports, from bad weather or other causes, the 

 direct currents were too weak to work the whole length. In construction it is 

 similar to the relay fixed on the bell instrument itself, but it consists of dupli- 

 cate bobbins and magnetic needles. 



1543. Wheatstone's Type Printing Instrument, 1841. 



Steel type punches are fixed at the extremities of separate radiating springs 

 placed round the circumference of a horizontal wheel, which is fixed on the 

 quickest wheel of the train of wheel work, and governed by a dead beat 

 escapement actuated by electro-magnets. The paper band passes under the 

 type, and the printing is performed by an electro ; magnet which causes a 

 hammer to strike the proper punch when it is opposite the paper. Alternate 

 layers of white and blackened paper are employed to receive the impressions 

 of the punch. 



1544. Theiler's Synchronous Type Printer, 1854. 



Two currents are required for each lettter, one to start the instrument and 

 another to print. The type- wheel returns to zero after the printing of each 

 letter, the sending and receiving instruments are made to act in unison, the 

 speed being regulated by a milled nut which is fixed on an arm attached to 

 the anchor of the escapement. Sending and receiving instruments. 



1545. Hughes' Type Printing Instrument. 



This is a purely synchronous instrument. The instruments at each end of 

 the line are timed to run as nearly as possible at the same speed, and regulated 

 by a spring vibrating in a circle. The type-wheel revolves continually, and 

 does not stop during the printing of a letter. One current only is necessary 

 for the latter operation, which is performed by the wheelwork liberated by an 

 electro-magnet of peculiar construction placed in the line circuit. 



Each time a letter is printed the type- wheel if out of time is corrected, that 

 is, moved backwards or forwards on its axis without disturbing the train of 

 wheels, so as to be synchronous with the instrument at the distant station. 

 39508. U 



