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* Philosophical Magazine； vol。 XI； p。 199 （March； 1832）。
Henry also discovered the phenomena of self induction and mutual induction。 A current sent through a wire in the second story of the building induced currents through a similar wire in the cellar two floors below。 In this discovery Henry anticipated Faraday though his results as to mutual induction were not published until he had heard rumors of Faraday's discovery； which he thought to be something different。
The attempt to send signals by electricity had been made many times before Henry became interested in the problem。 On the invention of Sturgeon's magnet there had been hopes in England of a successful solution； but in the experiments that followed the current became so weak after a few hundred feet that the idea was pronounced impracticable。 Henry strung a mile of fine wire in the Academy； placed an 〃intensity〃 battery at one end； and made the armature strike a bell at the other。 Thus he discovered the essential principle of the electric telegraph。 This discovery was made in 1831； the year before the idea of a working electric telegraph flashed on the mind of Morse。 There was no occasion for the controversy which took place later as to who invented the telegraph。 That was Morse's achievement； but the discovery of the great fact； which startled Morse into activity； was Henry's achievement。 In Henry's own words： 〃This was the first discovery of the fact that a galvanic current could be transmitted to a great distance with so little a diminution of force as to produce mechanical effects； and of the means by which the transmission could be accomplished。 I saw that the electric telegraph was now practicable。〃 He says further； however： 〃I had not in mind any particular form of telegraph； but referred only to the general fact that it was now demonstrated that a galvanic current could be transmitted to great distances； with sufficient power to produce mechanical effects adequate to the desired object。〃*
* Deposition of Joseph Henry； September 7； 1849； printed in Morse； 〃The Electra…Magnetic Telegraph〃； p。 91。
Henry next turned to the possibility of a magnetic engine for the production of power and succeeded in making a reciprocating…bar motor； on which he installed the first automatic pole changer； or commutator； ever used with an electric battery。 He did not succeed in producing direct rotary motion。 His bar oscillated like the walking beam of a steamboat。
Henry was appointed in 1839。 Professor of Natural Philosophy in the College of New Jersey； better known today as Princeton University。 There he repeated his old experiments on a larger scale； confirmed Steinheil's experiment of using the earth as return conductor； showed how a feeble current would be strengthened； and how a small magnet could be used as a circuit maker and breaker。 Here were the principles of the telegraph relay and the dynamo。
Why； then； if the work of Henry was so important； is his name almost forgotten； except by men of science； and not given to any one of the practical applications of electricity？ The answer is plain。 Henry was an investigator； not an inventor。 He states his position very clearly： 〃I never myself attempted to reduce the principles to practice； or to apply any of my discoveries to processes in the arts。 My whole attention exclusive of my duties to the College； was devoted to original scientific investigations； and I left to others what I considered in a scientific view of subordinate importancethe application of my discoveries to useful purposes in the arts。 Besides this I partook of the feeling common to men of science； which disinclines them to secure to themselves the advantages of their discoveries by a patent。〃
Then； too； his talents were soon turned to a wider field。 The bequest of James Smithson； that farsighted Englishman； who left his fortune to the United States to found 〃the Smithsonian Institution； for the increase and diffusion of knowledge among men；〃 was responsible for the diffusion of Henry's activities。 The Smithsonian Institution was founded at Washington in 1846； and Henry was fittingly chosen its Secretary； that is； its chief executive officer。 And from that time until his death in 1878； over thirty years； he devoted himself to science in general。
He studied terrestrial magnetism and building materials。 He reduced meteorology to a science； collecting reports by telegraph； made the first weather map； and issued forecasts of the weather based upon definite knowledge rather than upon signs。 He became a member of the Lighthouse Board in 1852 and was the head after 1871。 The excellence of marine illuminants and fog signals today is largely due to his efforts。 Though he was later drawn into a controversy with Morse over the credit for the invention of the telegraph； he used his influence to procure the renewal of Morse's patent。 He listened with attention to Alexander Graham Bell； who had the idea that electric wires might be made to carry the human voice； and encouraged him to proceed with his experiments。 〃He said；〃 Bell writes； 〃that he thought it was the germ of a great invention and advised me to work at it without publishing。 I said that I recognized the fact that there were mechanical difficulties in the way that rendered the plan impracticable at the present time。 I added that I felt that I had not the electrical knowledge necessary to overcome the difficulties。 His laconic answer was； 'GET IT！' I cannot tell you how much these two words have encouraged me。〃
Henry had blazed the way for others to work out the principles of the electric motor； and a few experimenters attempted to follow his lead。 Thomas Davenport； a blacksmith of Brandon； Vermont； built an electric car in 1835； which he was able to drive on the road； and so made himself the pioneer of the automobile in America。 Twelve years later Moses G。 Farmer exhibited at various places in New England an electric…driven locomotive； and in 1851 Charles Grafton Page drove an electric car； on the tracks of the Baltimore and Ohio Railroad； from Washington to Bladensburg； at the rate of nineteen miles an hour。 But the cost of batteries was too great and the use of the electric motor in transportation not yet practicable。
The great principle of the dynamo； or electric generator； was discovered by Faraday and Henry but the process of its development into an agency of practical power consumed many years； and without the dynamo for the generation of power the electric motor had to stand still and there could be no practicable application of electricity to transportation； or manufacturing； or lighting。 So it was that； except for the telegraph； whose story is told in another chapter； there was little more American achievement in electricity until after the Civil War。
The arc light as a practical illuminating device came in 1878。 It was introduced by Charles F。 Brush； a young Ohio engineer and graduate of the University of Michigan。 Others before him had attacked the problem of electric lighting； but lack of suitable carbons stood in the way of their success。 Brush overcame the chief difficulties and made several lamps to burn in series from one dynamo。 The first Brush lights used for street illumination were erected in Cleveland； Ohio； and soon the use of arc lights became general。 Other inventors improved the apparatus； but still there were drawbacks。 For outdoor lighting and for large halls they served the purpose； but they could not be used in small rooms。 Besides； they were in series； that is； the current passed through every lamp in turn； and an accident to one threw the whole series out of action。 The whole problem of indoor lighting was to be solved by one of America's most famous inventors。
The antecedents of Thomas Alva Edison in America may be traced back to the time when Franklin was beginning his career as a printer in Philadelphia。 The first American Edisons appear to have come from Holland about 1730 and settled on the Passaic River in New Jersey。 Edison's grandfather； John Edison； was a Loyalist in the Revolution who found refuge in Nova Scotia and subsequently moved to Upper Canada。 His son； Samuel Edison； thought he saw a moral in the old man's exile。 His father had taken the King's side and had lost his home； Samuel would make no such error。 So； when the Canadian Rebellion of 1837 broke out； Samuel Edison； aged thirty…three； arrayed himself on the side of the insurgents。 This time； however； the insurgents lost； and Samuel was obliged to flee to the United States； just as his father had fled to Canada。 He finally settled at Milan； Ohio； and there； in 1847； in a little brick house； which is still standing； Thomas Alva Edison was born。
When the boy was seven the family moved to Port Huron； Michigan。 The fact that he attended school only three months and soon became self…supporting was not due to poverty。 His mother； an educated woman of Scotch extraction； taught him at home after the schoolmaster reported that he was 〃addled。〃 His desire for money to spend on chemicals for a laboratory which he had fitted up in the cellar led to his first venture in business。 〃By a great amount of persistence；〃 he says； 〃I got permission to go on the local train as newsboy。 The local train