ADDEESS OF PROP. A. GRAY. 59 



For the telegraph, and for electro-magnetic machines, what was 

 now wanted was not discovery, but invention, not the ascertainment 

 of principles, but the devising of methods. These, the proper 

 subjects of patent, have been supplied in various ways and, as to 

 the telegraph, with wonderful efficiency; in Europe, by the trans- 

 mission of signs through the motion of a magnetic needle; in 

 America, by the production of sounds or records by the electro- 

 magnet. MORSE was among the first to undertake the enterprise, 

 and, when directed to the right way through Professor GALE'S 

 acquaintance with HENRY'S published researches, he carried the 



1820. AMPERE discovered that two wires through which currents are passing in the 

 same direction attract, and in opposite directions repel, each other; and thence 

 he inferred that magnetism consists in the attraction of electrical currents 

 revolving at right angles to the line joining the two poles of the magnet, and 

 is produced in a bar of steel or iron by induction from a series of electrical 

 currents revolving in the same direction at right angles to the axis of the bar. 



1820. SCHWEIGGER in the same year produced the galvanometer. 



1825. STURGEON made the electro-magnet by bending the bar, or rather a piece 

 of iron wire, into the form of a horse-shoe, covering it with varnish to insulate 

 it, and surrounding it with a helix of wire the turns of which were at a dis- 

 tance. 



1829-'l830. HENRY, in accordance with the theory of AMPERE, produced the intensity 

 or spool-wound magnet, insulating the wire instead of the rod or bar, and 

 covering the whole surface of the iron with a series of coils in close contact. 

 He extended the principle to the full by winding successive strata of insulated 

 wire over each other, thus producing a compound helix formed of a long wire 

 of many coils. At the same time he developed the relation of the intensity 

 magnet to the intensity battery, and their relations to the magnet of quantity. 

 He thus made the electro-magnet capable of transmitting power to a long 

 distance, demonstrated the principle and perfected the magnet applicable to 

 the purpose, was the first actually to magnetize a piece of iron at a distance, 

 and to demonstrate and declare the applicability of the electro-magnet to 

 telegraphy at a distance. Using the terminal short-circuit magnet of quantity, 

 and the armature as the signaling device, he was the first to make by it 

 acoustic signals, sounding a bell at a distance by means of the electro-magnet. 



1833. WEBER discovered that the conducting-wires of an electric telegraph could 

 be left without insulation except at the points of support. 



1833. GAUSS ingeniously arranged the application of a dual sign in such manner 

 as to produce a true alphabet for telegraphy. 



1836. DANIEI/L invented and brought into use a constant galvanic battery. 



1837. STEINHEIL discovered that the earth may form the returning half of the 

 circuit, so that a single conducting wire suffices for telegraphy. 



1837. MORSE adopted, through the agency of Dr. LEONARD GALE, the principle of 

 the HENRY electro-magnet, and made of the armature a recording instrument. 



1838. MORSE devised his " dot and dash " alphabet, a great improvement upon the 

 GAUSS and STEINHEIL alphabets. 



1844. MORSE suggested and brought into use the system of relay-magnets, and 

 relay-circuits, to reinforce the current. 



