6 BELL SYSTEM TECHNICAL JOURNAL 



mand our admiration. Of course, until the ch'namo was invented 

 at a later date, and a substantial electric current became a\-ailable, 

 the motor could not be much more than he characterized it, "a 

 philosophical toy." 



Henry also became interested in a determining whether an electro- 

 magnet could be operated from a distance so that the doing of some 

 work — for example the ringing of a bell — could be controlled from a 

 distant station. From his investigations directed to this end, Henry 

 was. the first to appreciate that the effect of the resistance of long 

 lengths of wire to the passage of electric current could be minimized 

 by properly proportioning the battery and the magnet windings to the 

 length and resistance of the line wires. 



ElTorts had been made by others prior to Henry's time to devise 

 successful electric telegraphs. They had failed, however, because 

 they did not know^ how to proportion their magnets and their batteries 

 so as to operate over any substantial length of line. The literature of 

 that time contains a number of demonstrations of the impossibility 

 of operating an electric telegraph, because scientists could arrange 

 instruments which would operate successfully when separated by 

 a few feet, or even one hundred feet, but they would not work at a 

 distance of thousands of feet because of the resistance of the long 

 line wire. 



What Henry did was to determine the proportioning of the various 

 parts of the system so as to secure operation. He found, when his 

 magnet was connected by a short wire to the battery, that the greatest 

 magnetizing effect was obtained by joining the cells of the battery in 

 parallel, but that a series arrangement of the battery would give the 

 greatest pull if a long wire (a length of a mile or more w^as used in 

 some of his experiments) carried the current. He also obtained the 

 best operation over a short line when the magnet winding consisted 

 of several distinct coils, all connected in multiple; and for operation 

 over a long line he found it best either to connect these coils in series 

 or to apply to the magnet a single long w'inding. Henry was there- 

 fore the first to produce an electric telegraph, and more than that, 

 the transmission of electrical energy to a distance. That first tele- 

 graph paved the way for all the telegraph systems, all the ocean 

 cable systems, and contained the principle of all telephone call bells. 



One of Henry's greatest discoveries from the standpoint of electrical 

 science, but a discovery in which he must yield the first place to 

 Faraday, is that of mutual induction — the fact that a wire w^hen 

 moving with respect to a magnetic field has an electromotive force 

 generated in it. Although Henry made his discovery independently 



