352 HENEY AND THE TELEGRAPH. 



February 23, 1843; and tbo Morse approiiriation was secured, by passing tbe Senate, 

 March 3,' 1843. 



Very sbortly after tbis successful issue, Prof. James C, Fisber, wbo in tbe absence 

 of Dr. Gale bad taken bis place in assisting Professor Morse, wrote to Henry explain- 

 ing tbe luetbod proxiosed for insulating tbe wires and laying tbe line of conductors 

 underground, and asking advice as to tbe best method of wrapxiiug. To tbis commu- 

 nication Henry replied by letter dated — 



'' Princeton, April 17, 1843, 

 " De4K Sir : A friend of mine in Trenton has a machine for winding wire of which 

 he promised to give a descrii)tiou. I will write to you on the subject and send you a 

 copy of bis answer. Tbe greatest j)ractical difficulty yon will have to contend with, 

 I should think, will be the insulation of the wires. Twine is a partial conductor, and 

 by making tbe surface sufficiently extended, lateral transmission will take place to 

 some extent. Tbe loss however on this account can only be determined by direct 

 exx^eriment with extended wire. It will jirobably increase with an increasing ratio ; 

 first on account of the greater surface of contact, and secondly because electricity 

 of greater tension will be required to send the current through the longer wire. In 

 order to diminish tbe number of x^oints of contact, it might x^erhaps be well to wrap 

 around each wire — besides its continuous covering, an extra strand of coarse twine, 

 with the several turns at a distance from each other. . . ." 



When Professor Morse, in August, 1843, received IGO miles of covered copper wire, 

 designed to form two indexiendent circuits, each of a double line of 40 miles in extent, 

 to reach from Washington to Baltimore (one x^air for the outgoing circuit and the other 

 for the return circuit), he invited Henry and others to be present at a xn-elimiuary ex- 

 periment in New York City, on the 8tb of August, to test tbe capacity of electrical 

 transmission. Tbis very interesting trial with so unusual a length of conductor would 

 for tbo first time decide tbe correctness of Henry's opinion that magnetization could be 

 effected "at the distance of a hundred miles or more by a single impulse." Tbis crit- 

 ical test — ^uever before attempted, Henry was unfortunately prevented from witnessing, 

 by reason of bis professional duties. Tbe experiment was eminently successful with 

 a battery of 100 Grove elements; and tbe magnet was operative with even half that 

 number. The following letter to Professor Morse expressed Henry's regrets at being 

 compelled to miss such an ox^x^ortunity : 



''Princetox, August 22, 1?43. 



"My Dear Sir: I hope you will pardon me for not before acknowledging the receix')t 

 of your kind letters of invitation to attend your galvanic exhibition. My time has 

 been so much occux>ied dmlng the last three weeks vrith an extra course of lectures 

 and our examination, and so little at my own disposal, that I was unable to say 

 whether I could be in the city on the day you mentioned or not. I did hope however 

 to get away, but the examination prevented. Dr. Torrey was also engaged, and could 

 not leave. I do not know however that I could have done much in the way of orig- 

 inal exx>eriments in the course of a single day. I am not rxuick in tbe x»rocess of in- 

 venting experiments unless my mind is thoroughly aroused to the subject by several 

 days' exclusive attention to the work, and then I am obliged to pause between each 

 effort.* I have not been able since I last saw you to devise a satisfactory process for 

 determining tbe velocity of galvanic electricity ; and on refiection I did not think it 

 worth tbe exx^ense which would be incurred, to have a machine constructed for the 

 mere rex)etition of the exx)eriments of Wheatstone. 



"I think it probable that I shall visit the city next week, as I shall be unemxiloyed 

 from this time until a week from next Monday. If there is any prospect of your 



*[An indication of the logical care bestowed by Henry on bis experimental work, and 

 the key to bis successes. He had little confidence in tbe x>rofit of empirical or " haxJ- 

 hazard" trials.] 



