FKOMENT'S ALPHABETIC TELEGRAPH. 



at two stations, s and s', connected as usual by a conducting 

 wire ; the instrument, being unemployed, the line- wire at both is 

 in connection with the alarum. Now let us suppose that s desires 

 to transmit a despatch to s'. In that case s having first turned 

 on the current, puts down any key whatever of his commutator, 

 the effect of which is that a current is transmitted upon the 

 line wire to s', which rings the alarum; then s' replies by 

 transmitting a return current in the same way to s, by which 

 s's alarum is rung. All being then prepared for the trans- 

 mission of the despatch, s puts down with his fingers succes- 

 sively the keys of his commutator upon which the successive 

 letters spelling the words of the despatch are engraved, and 

 simultaneously with this the indicator upon the dial of s' points 

 to the same letters, which are taken down by s'. At the end of 

 each word, s puts down the key marked with the cross. 



"When it is intended to transmit numerals, s puts down the 

 arrow just before he begins them, and the cross when he ends them. 

 Thus if it be desired to transmit the number 1854, s first puts 

 down the arrow, and then the keys marked A, H, E, and D succes- 

 sively, after which he again puts down the cross to indicate that 

 the number is finished. It remains now to explain how these 

 effects are produced. 



Within the case, and at some distance below the key-board, a 

 steel rod is extended, parallel to the line of keys, the length of 

 which corresponds with that of the row of keys. From this rod, 

 and at right angles to it, proceeds a series of short steel arms, one 

 under each key. In the bottom of each key, and at right angles 

 to it, is inserted a short projecting pin, which corresponds pre- 

 cisely in position with the short steel arm just mentioned. The 

 length of the arm, and that of the pin, taken together, is a little 

 less than the distance between the bottom of the key and the 

 steel rod when the key is not put down by the finger, the neces- 

 sary consequence of which is that in that position of the key the 

 rod may revolve, carrying the arm round with it unobstructed. 

 But when the key is put down by the finger, the bottom of it is 

 brought to a distance from the rod which is less than the sum of 

 the lengths of the projecting arm and the pin, and consequently 

 if the rod revolves, carrying with it the projecting arm while the 

 key is thus held down, the pin coming in the way of the arm 

 arrests it, and stops the further revolution of the steel rod. 



It is evident that if the projecting arms were all inserted in the 

 teel rod at the same side, or to speak with still more precision, if 

 their points of insertion lay in a line along the side of the rod 

 parallel to its axis, the pins of all the keys would arrest the 

 revolution of the rod in exactly the same position, and, as it 



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