While the line-builders were busy stretching telegraph wires into almost every city and town in the nation, others were perfecting the apparatus. Alfred Vail was a leading figure in this work. Already he had played a large part in designing and constructing the apparatus to carry out Morse's ideas, and he continued to improve and perfect until practically nothing remained of Morse's original apparatus. The original Morse transmitter had consisted of a porte-rule and movable type. This was cumbersome, and Vail substituted a simple key to make and break the circuit. Vail had also constructed the apparatus to emboss the message upon the moving strip of paper, but this he now improved upon. The receiving apparatus was simplified and the pen was replaced by a disk smeared with ink which marked the dots and dashes upon the paper.
As we have noticed, Morse took particular pride in the fact that the receiving apparatus in his telegraph was self-recording, and considered this as one of the most important parts of his system. But when the telegraph began to come into commercial use the operators at the receiving end noticed that they could read the messages from the long and short periods between the clicks of the receiving mechanism. Thus they were taking the message by ear and the recording mechanism was superfluous. Rules and fines failed to break them of the habit, and Vail, recognizing the utility of the development, constructed a receiver which had no recording device, but from which the messages were read by listening to the clicks as the armature struck against the frame in which it was set. Thus the telegraph returned in its elements to the form of Professor Henry's original bell telegraph.
With his bell telegraph and his relay Henry had the elements of a successful system. He failed, however, to develop them practically or to introduce them to the attention of the public. He was the man of science rather than the practical inventor. Alfred Vail, joining with Morse after the latter had conceived the telegraph, but before his apparatus was in practical form, was a tireless and invaluable mechanical assistant. His inventions of apparatus were of the utmost practical value, and he played a very large part in bringing the telegraph to a form where it could serve man effectively. After success had been won Morse did not extend to Vail the credit which it seems was his due.