Morse knew little of the work of other experimenters in the field of
electricity and Gale was able to tell Morse what had been learned by
others. Particularly he brought to Morse's attention the discoveries
of another American, Prof. Joseph Henry.

The electro-magnet which actuated the receiving instrument in the
crude set in use by Morse in 1835 had but a few turns of thick
wire. Professor Henry, by his experiments five years earlier, had
demonstrated that many turns of small wire made the electro-magnet far
more sensitive. Morse made this improvement in his own apparatus. In
1832 Henry had devised a telegraph very similar to that of Morse by
which he signaled through a mile of wire. His receiving apparatus
was an electro-magnet, the armature of which struck a bell. Thus the
messages were read by sound, instead of being recorded on a moving
strip of paper as by Morse's system. While Henry was possibly the
ablest of American electricians at that time, he devoted himself
entirely to science and made no effort to put his devices to practical
use. Neither did he endeavor to profit by his inventions, for he
secured no patents upon them.

Professor Henry realized, in common with Morse and others, that if
the current were to be conducted over long wires for considerable
distances it would become so weak that it would not operate a
receiver. Henry avoided this difficulty by the invention of what is
known as the relay. At a distance where the current has become
weak because of the resistance of the wire and losses due to faulty
insulation, it will still operate a delicate electro-magnet with a
very light armature so arranged as to open and close a local circuit
provided with suitable batteries. Thus the recording instrument may
be placed on the local circuit and as the local circuit an opened and