ELECTRIC TELEGKAPH. 



instruments which print in the ordinary letters the dispatch at 

 the station to which it is addressed, by means of a power worked 

 at the station from which it is transmitted. In a certain sense, 

 this is accomplished by the three forms of telegraph described in 

 (202, 203, and 204) ; but in these cases the dispatch is printed 

 or written in cipher, which is attended with the inconvenience of 

 being understood only by those who possess, and are sufficiently 

 familiar with the key. The process of deciphering it, and 

 writing it in common characters, occupying more or less 

 time, for some purposes, such for example as that of journalism, 

 this time must be taken into account in estimating the 

 practical celerity of communications, inasmuch as the dispatch 

 until so interpreted, is not available to the parties to whom it is 

 addressed. 



A telegraph which instead of impressing on paper characters in 

 cipher, would impress the characters of common letter-press, even 

 though these should be transmitted and impressed at a slower rate 

 than that of the transmission of the characters in cipher, might 

 nevertheless be, in effect, more expeditious, more time being 

 saved by superseding the process of interpreting the cipher than 

 is lost by the relative slowness of the transmission. 



It is evident that these observations, being general, are 

 applicable, not only to the instrument we are now about .to des- 

 cribe, but to all others of the same class. 



219. House's printing telegraph, like all other telegraphic 

 instruments, consists of two distinct parts, a commutating 

 apparatus to govern the transmission of the current, and a 

 printing apparatus upon which the current arriving from a 

 distant station operates. 



The manner in which the transmission of the current is con- 

 trolled by the keys of the finger-board, is substantially the same 

 as in Froment's telegraph already described. The wheel, how- 

 ever, that produces by its revolution the pulsations of the current, 

 is moved, not as in Froment's by clock-work, but by the foot of the 

 operator, acting upon a treddle like that of a lathe which is seen 

 under the case of the commutator in the fig. 89 (p. 81). 



The rotation of this wheel is arrested at the point corres- 

 ponding to any desired letter, by putting down with the finger 

 the key upon which that letter is engraved, in exactly the 

 same manner and by the same mechanical expedient as in 

 Froment's telegraph. 



The keys, upon the key-board of this instrument, govern by 



means of the pulsations of the current the motion and position of 



a dial or wheel at a distant station, inscribed with similar 



characters in the same manner as has been already explained in 



56 



