HENRY AND THE TEIlEGRAPH. 353 



repeating any of your experiments previous to that time, I will be witli you on any 

 day you may api)oint. 



"With much respect and esteem, 

 "Yours truly, 



''Joseph Henry." 



The answer to this, or whether any further preliminary experiments were jointly 

 performed on the IfiO miles of wire, does not appear. As tlie line of wires between 

 Washington and Baltimore was being laid, Henry, anxious to emphasize the importance 

 of keeping the separate wires at some distance apart throughout their circuit, ad- 

 dressed to Professor Morse the following friendly letter on the subject: 



"Princeton, January 24, 1844. 

 "My Dear Sir: I am anxious to hear from you in reference to the telegraph, and 

 I have intended to write to you on the subject for a mouth past, but extra college 

 duties have occupied all my thoughts and all my time since the beginning of the 

 present term. During the last vacation I occupied myself as usual with my investi- 

 gations in electricity, and among other results, I arrived at one which I think may 

 have an important bearing on the success of the telegraph. It is tbis: while a current 

 of electricity is passing through a wire, one part of the conductor is constantly plus to 

 any other part which succeeds it, the difference in the degree of the electrical state 

 constantly increasing as the distance of the two points is greater. The maximum 

 diiference is therefore at the two ends ; and when the two extremities of long wires 

 are brought into near approximation, there is a great tendency in the elecricity to cut 

 across from the one to the other. This tendency is not due as has been supposed, 

 merely to the great resistance of the long wire and the cross-cut offering a less resist- 

 ing channel, but to the fact of the one part being j)ositive and the other negative, and 

 the consequent great attraction of the electricity in the one part for the unsaturated 

 matter in the other. ... On reading your letter on the subject of the telegraph 

 in the newspapers, I was struck with the idea that you had probably met with the 

 very difficulty my researches have led me to anticipate. If this is the case, and 

 your insulation is not found sufficient, you have no cause to blame yourself, since the 

 previous state of knowledge on the subject of electricity could not lead you to suspect 

 such a condition of things. 



"With much respect, 



Yours truly, 



"Joseph Henry." 



The danger apprehended by Henry was realized ; and of the nine miles of quadruple 

 conductors laid in the ground. Professor Gale had already discovered that the galvanic 

 current could not be carried through a single mile; a result partly due to the injury 

 done to the insulation of the wires at some points, in the process of enveloping them 

 in a tube, and partly to the energetic induction from the "extra current" first dis- 

 covered by Henry. In a couple of weeks. Professor Morse wrote to Henry as follows : 



"Baltimore, February 7, 1844. 

 "My Dear Sir: You must think it strange that I have not answered your letter 

 of the 24th ultimo before this ; but I have this moment received it in passing through 

 this place on my way to New York, which I trust will be a sufficient apology for my 

 apparent neglect. I have read your letter with much interest, and it has determined 

 me to make you a visit on my return from New York, which will be the beginning of 

 the week, perhaps on Tuesday mommg, the 13th instant. ... I found the diffi- 

 culty which you apprehend in the insulation of my wires; but this I will explain 

 when I have the pleasure of seeing you. 



" In the mean time, believe me, with sincere respect, 

 "Your most obedient servant, 



"Samuel F. B. Moesk." 

 S. Mis. 59 23 



