He was present at the exhibition of Morse's invention on the 2d of September, 1837, and he at once grasped its great possibilities.

After becoming satisfied that Morse's device of the relay would permit of operation over great distances, he expressed a desire to become associated with the inventor in the perfecting and exploitation of the invention.

His father was the proprietor of the Speedwell Iron Works in Morristown, and young Vail had had some experience in the manufacture of mechanical appliances in the factory, although he had taken the theological course at the University with the intention of entering the Presbyterian ministry.

He had abandoned the idea of becoming a clergyman, however, on account of ill-health, and was, for a time, uncertain as to his future career, when the interest aroused by the sight of Morse's machine settled the matter, and, after consulting with his father and brother, he entered into an agreement with Morse on the 23d day of September, 1837.
In the contract drawn up between them Vail bound himself to construct, at his own expense, a complete set of instruments; to defray the costs of securing patents in this country and abroad; and to devote his time to both these purposes.

It was also agreed that each should at once communicate to the other any improvement or new invention bearing on the simplification or perfecting of the telegraph, and that such improvements or inventions should be held to be the property of each in the proportion in which they were to share in any pecuniary benefits which might accrue.
As the only way in which Morse could, at that time, pay Vail for his services and for money advanced, he gave him a one-fourth interest in the invention in this country, and one half in what might be obtained from Europe.