APPENDIX TO THE REPORT OF THE COMMITTEE. 



STATEMENT OF PROF. HENRY, 



IN RELATION TO 



THE HISTORY OF THE ELECTRO-MAGNETIC TELEGRAPH. 



In the beginning of my deposition I was requested to give a sketch of 

 the history of electro-magnetism having a bearing on the telegraph, an,d 

 the account I then gave from memory, I have since critically examined 

 and find it fully corroborated by reference to the original authorities. My 

 sketch, which was the substance of what I had been in the habit of giving 

 in my lectures, was necessarily very concise, and almost exclusively con- 

 fined to one class of facts, namely, those having a direct bearing on Mr. 

 Morse's invention, and my paper in Silliman's Journal was likewise very 

 brief and intended merely for scientific men. In order, therefore, to set 

 forth more clearly in what my own improvements consisted, it may be 

 proper to give a few additional particulars respecting some points in the 

 progress of discovery, illustrated by wood cuts. 



There are several forms of the electrical telegraph ; first, that in which 

 frictional electricity has been proposed to produce sparks and motion of 

 pith balls at a distance. 



Second, that in which galvanism has been employed to produce signals 

 by means of bubbles of gas from the decomposition of water. 



Third, that in which electro-magnetism is the motive power to produce 

 motion at a distance ; and again, of the latter there are two kinds of tele- 

 graphs, those in which the intelligence is indicated by the motion of a 

 magnetic needle, and those in which sounds and permanent signs are made 

 by the attraction of an electro-magnet. The latter is the class to which 

 Mr. Morse's invention belongs. The following is a brief exposition of the 

 several steps which led to this form of the telegraph. 



The first essential fact, as I stated in my testimony, which rendered 

 the electro-magnetic telegraph possible was discovered*by Oersted, in the 



