CHAP. IH.] 



ELECTRIC TELEGRAPHY. 



569 



the circumference, that is to say when the handle passes from one 

 letter to another, the pinion makes half a revolution, and also the 



Fiu. 3t5o. Nutt and Gamble's letter-telegraph, 184(5. 



cylinder cc. On the iron column BB are fixed hy similar poles the 

 permanent magnets a a a ranged in two series, one presenting to the 



FIG. 367. Siemens' and Halske's dial telegraph. 



cylinder c the north-seeking pole on one side of the cylinder, and the 

 other series the south-seeking pole on the other side ; and it is by 



