HISTORY AND PROGRESS. 55 



cylinder by the slide-valve, moves horizontally, and is in 

 connection with the lever of an anchor- escapement engaging 

 with the teeth of the scape- wheel of the printing machine. 



The scape- wheel has fourteen teeth, and requires, there- 

 fore, twenty-eight movements of the lever to complete a 

 revolution. A steel type- wheel revolves with the same shaft 

 as the scape- wheel, its circumference being furnished with 

 twenty- eight equidistant projections, on which are engraved 

 the letters of the alphabet, a dot, and a dash. The shaft also 

 carries a little drum with letters painted on it in the same 

 order as those on the type- wheel, by which the operator may 

 read off the message when the type- wheel is not printing. 



On the upper surface of the type- wheel, at the extreme 

 edge, are twenty- eight teeth, against which plays a small 

 steel arm, attached to a metal cap, turned by friction on a 

 shaft revolving in the reverse direction. When the type- 

 wheel is in motion, this arm plays over the teeth, but as 

 soon as the wheel is stopped, falls in between them, which it 

 has not time to do during the revolution. By falling in the 

 teeth of the type-wheel, the arm allows the cap to revolve 

 with its shaft, and by means of two pins, to release a detent, 

 which, in its turn, permits an eccentric to revolve. A con- 

 necting-rod from the eccentric, pulls the paper strip to the 

 type- wheel and prints the letter. 



An ingenious arrangement is also made for the progres- 

 sion of the paper, by means of a ratchet-wheel and clicks 

 attached to a notched drum over which the paper passes. 



The line from Philadelphia to New York was the first on 

 which this instrument was used. It found very general 

 adoption on the American lines, after the year, 1849, and 

 is still to be found at work. It is said to be much less liable 

 to get out of order than would be judged, at first sight, from 

 the complication of the receiving apparatus. 



51. Hughes' Roman-type printing Telegraph. The essen- 

 tial principle of this highly ingenious system is the syn- 

 chronous movements of type- wheels at two or more stations, 

 and of the power to press a strip of paper at each of the 

 stations simultaneously against the types on the correspond- 



