Shortly after his return from abroad, on April 24, Morse wrote the following letter to Professor Henry at Princeton:—
My Dear Sir,—On my return a few days since from Europe, I found directed to me, through your politeness, a copy of your valuable "Contributions," for which I beg you to accept my warmest thanks. The various cares consequent upon so long an absence from home, and which have demanded my more immediate attention, have prevented me from more than a cursory perusal of its interesting contents, yet I perceive many things of great interest to me in my telegraphic enterprise.
I was glad to learn, by a letter received in Paris from Dr. Gale, that a spool of five miles of my wire was loaned to you, and I perceive that you have already made some interesting experiments with it.
In the absence of Dr. Gale, who has gone South, I feel a great desire to consult some scientific gentleman on points of importance bearing upon my Telegraph, which I am about to establish in Russia, being under an engagement with the Russian Government agent in Paris to return to Europe for that purpose in a few weeks. I should be exceedingly happy to see you and am tempted to break away from my absorbing engagements here to find you at Princeton. In case I should be able to visit Princeton for a few days a week or two hence, how should I find you engaged? I should come as a learner and could bring no "contributions" to your stock of experiments of any value, nor any means of furthering your experiments except, perhaps, the loan of an additional five miles of wire which it may be desirable for you to have.
I have many questions to ask, but should be happy, in your reply to this letter, of an answer to this general one: Have you met with any facts in your experiments thus far that would lead you to think that my mode of telegraphic communication will prove impracticable? So far as I have consulted the savants of Paris, they have suggested no insurmountable difficulties; I have, however, quite as much confidence in your judgment, from your valuable experience, as in that of any one I have met abroad. I think that you have pursued an original course of experiments, and discovered facts of more value to me than any that have been published abroad.
Morse was too modest in saying that he could bring nothing of value to Henry in his experiments, for, as we shall see from Henry's reply, the latter had no knowledge at that time of the "relay," for bringing into use a secondary battery when the line was to stretch over long distances. This important discovery Morse had made several years before.
PRINCETON; May 6, 1889.
DEAR SIR,—Your favor of the 24th ult. came to Princeton during my absence, which will account for the long delay of my answer. I am pleased to learn that you fully sanction the loan which I obtained from Dr. Gale of your wire, and I shall be happy if any of the results are found to have a practical bearing on the electrical telegraph.
It will give me much pleasure to see you in Princeton after this week. My engagements will not then interfere with our communications on the subject of electricity. During this week I shall be almost constantly engaged with a friend in some scientific labors which we are prosecuting together.
I am acquainted with no fact which would lead me to suppose that the project of the electro-magnetic telegraph is unpractical; on the contrary, I believe that science is now ripe for the application, and that there are no difficulties in the way but such as ingenuity and enterprise may obviate. But what form of the apparatus, or what application of the power will prove best, can, I believe, be only determined by careful experiment. I can say, however, that, so far as I am acquainted with the minutiae of your plan, I see no practical difficulty in the way of its application for comparatively short distances; but, if the length of the wire between the stations is great, I think that some other modification will be found necessary in order to develop a sufficient power at the farther end of the line.