BIOGRAPHICAL MEMOIR OF JOSEPH HEXRY. 159 



with varnisli to insulate it, and suiTOuuding it with a helix of 

 vfirc the turns of which were at a distance. 



1829-1830. Ilenry, in accordance with the theory of Ampere, produced 

 the intensity or spool-wound niagnet, insulating the wire in- 

 stead of the rod or har, and covering the whole surface of tlie 

 iron with a series of coils in close contact. He extended the 

 I>rinciple to the full by vrinding successive strata of insulated 

 wire over each other, thus producing a compound helix fonued 

 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 tlie 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 siguiiling device, he was the lirst 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 tele- 

 graph 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. 



1830. Daniel 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 

 telegrai^hy. 



1837. Morse adopted, through the agency of Dr. Gale, the principle of 



the Henry electromagnet, and the armature made of a record- 

 ing instrument. 



1838. Morse devised his "dot and dash" alphabet, a great improvement 



upon the Gauss and Steinheil alphabets. 

 1814. Morse suggested and brought into use the system of relay-mag- 

 uets, and relay-circuits, to re-einforce the current. 



NOTE II. 



LETTER FRO:.I PROFESSOR HENRY TO THE REY. S. B. DOD, GIVING A 

 SKETCH OF SCIENTIFIC RESEARCHES AT PRINCETON. 



[From the Princeton Memorial of Professor Henry.] 



My Dear Sir : In compliance with your request that I would give 

 an account of my scientilic researches during my connection with the 

 College of Xev,- Jersey, I furnish the following brief statement of my 

 labors within the period mentioned: 



I. Previous to my call from the Albany Academy to a professorship 

 in the College of New Jersey, I had made a series of researches on ele<5- 

 tro-magnetism, in which I develo])ed the i)rincii)les of the electro-mag- 

 net and the means of accumulating the magnetic power to a great ex- 

 tent, and had also applied this power in the invention of the lirst elec- 

 tro-nuignetic machine; that is, a mechanical contrivance by v>hich elec- 

 tro-magnetism was applied as a motive i)ower. 



