the applicability of his discovery to the electro-magnetic telegraph 

 At that time he published no description of his experiments, but did so 

 a number of years later. There are also accounts of several eye- 

 witnesses to them, the following from a letter of James Hall to Henry, 

 January 19, 1856. 



"While a student of the Rensselaer School, in Troy, New York, in August, 1832, I 

 visited Albany with a friend, having a letter of introduction to you from Professor 

 Eaton. Our principal object was to see your electro-magnetic apparatus, of which we 

 had heard much, and at the same time the library and collections of the Albany 

 Institute. 



"You showed us your laboratory in a lower story or basement of the building, 

 and in a larger room in an upper story some electric and galvanic apparatus, with 

 various philosophical instruments. In this room, and extending around the same, 

 was a circuit of wire stretched along the wall, and at one termination of this, in the 

 recess of a window, a bell was fixed, while the other extremity was connected with a 

 galvanic apparatus. 



"You showed us the manner in which the bell could be made to ring by a current 

 of electricity, transmitted through this wire, and you remarked that this method 

 might be adopted for giving signals, by the ringing of a bell at the distance of many 

 miles from the point of its connexion with the galvanic apparatus." '- 



And Dr. Orlando Meads, a former student of the Albany Academy, in 

 1863 in a discourse commemorating an anniversary of the Academy, 

 thus referred to the scenes he had witnessed one-third of a century 

 before : 



"The older students of the Academy in the years 1830, 1831, and 1832, and other? 

 who witnessed his experiments which at that time excited so much interest in this 

 city, will remember the long coils of wire which ran circuit upon circuit for more than 

 a mile in length around one of the upper rooms in the Academy, for the purpose of 

 illustrating the fact that a galvanic current could be transmitted through its whole 

 length so as to excite a magnet at the farther end of the line, and thus move a steel 

 bar which struck a bell." ^^ 



Henry had two applications of his electro-magnets in mind: first, 

 the production of a machine to be moved by electro-magnetism and, 

 second, the transmission of or calling into action power at a distance. 



"... for the purpose of experimenting in regard to the second, I arranged around 

 one of the upper rooms in the Albany Academy a wire of more than a mile in length, 

 through which I was enabled to make signals by sounding a bell." ^^ 



Henry later used the grounded circuit, another close parallel to the 

 form taken in the practical development of the telegraph. This 

 principle, however, had been used years earlier in electrostatic tele- 

 graphs and in firing gun powder at a distance, e.g., by Cavallo in 

 1794-5 and Salva in 1798.^^ 



^''Annual Report Smithsonian Institution 1857, p. 96. 



13 A Memorial of Joseph Henry, published by Order of Congress. 1880, p. 380. 

 " SW, Vol. 2, p. 434, 1857. 



^^ A Historv of Electric Telegraphy to the Year 1837, bv J. J. Fahie, 1884, pp. 99 

 and 108. 



12 



