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A History of Wireless Telegraphy (2nd edition, revised), J. J. Fahie, 1901, pages 10-13:

PROFESSOR  MORSE--1842.

    The idea of a wireless telegraph next appears to have presented itself to Professor Morse. In a letter to the Secretary of the Treasury, which was laid before the House of Representatives on December 23, 1844, he says:--
    "In the autumn of 1842, at the request of the American Institute, I undertook to give to the public in New York a demonstration of the practicability of my telegraph, by connecting Governor's Island with Castle Garden, a distance of a mile; and for this purpose I laid my wires properly insulated beneath the water. I had scarcely begun to operate, and had received but two or three characters, when my intentions were frustrated by the accidental destruction of a part of my conductors by a vessel, which drew them up on her anchor, and cut them off. In the moments of mortification I immediately devised a plan for avoiding such an accident in future, by so arranging my wires along the banks of the river as to cause the water itself to conduct the electricity across. The experiment, however, was deferred till I arrived in Washington; and on December 16, 1842, I tested my arrangement across the canal, and with success. The simple fact was then ascertained that electricity could be made to cross a river without other conductors than the water itself; but it was not until the last autumn that I had the leisure to make a series of experiments to ascertain the law of its passage. The following diagram will serve to explain the experiment:--
Fig. 1

    "A, B, C, D, are the banks of the river; N, P, is the battery; G is the galvanometer; w w, are the wires along the banks, connected with copper plates, f, g, h, i, which are placed in the water. When this arrangement is complete, the electricity, generated by the battery, passes from the positive pole, P to the plate h, across the river through the water to plate i, and thence around the coil of the galvanometer to plate f, across the river again to plate g, and thence to the other pole of the battery, N.
    "The distance across the canal is 80 feet; on August 24 the following were the results of the experiment:--

 
No. of the experiment.1st.2nd.3rd.4th.5th.6th.
No. of cups in battery
Length of conductors, w, w
Degrees of motion of galvanometer
Size of copper plates, f, h, g, i		 14
400
32 & 24
5 by 2½ ft.		 14
400
13½ & 4½
16 by 13 in.		 14
400
1 & 1
6 by 5 in.		 7
400
24 & 13
5 by 2½ ft.		 7
300
29 & 21
5 by 2½ ft.		 7
200
21½ & 15
5 by 2½ ft.

    "Showing that electricity crosses the river, and in quantity in proportion to the size of the plates in the water. The distance of the plates on the same side of the river from each other also affects the result. Having ascertained the general fact, I was desirous of discovering the best practical distance at which to place my copper plates, and not having the leisure myself, I requested my friend Professor Gale to make the experiments for me. I subjoin his letter and the results. 13

"'NEW YORK, Nov. 5th, 1844.    

    "'MY  DEAR  SIR,--I send you herewith a copy of a series of results, obtained with four different-sized plates, as conductors to be used in crossing rivers. The batteries used were six cups of your smallest size, and one liquid used for the same throughout. I made several other series of experiments, but these I most rely on for uniformity and accuracy. You will see, from inspecting the table, that the distance along the shores should be three times greater than that from shore to shore across the stream; at least, that four times the distance does not give any increase of power. I intend to repeat all these experiments under more favourable circumstances, and will communicate to you the results.--Very respectfully,           L. D. GALE.
    "'Professor S. F. B. MORSE,
          Superintendent of Telegraphs.'

    "As the results of these experiments, it would seem that there may be situations in which the arrangements I have made for passing electricity across rivers may be useful, although experience alone can determine whether lofty spars, on which the wires may be suspended, erected in the rivers, may not be deemed the most practical. The experiments made were but for a short distance; in which, however, the principle was fully proved to be correct. It has been applied under the direction of my able assistants, Messrs Vail and Rogers, across the Susquehanna river, at Havre-de-Grace, with complete success, a distance of nearly a mile." 14

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13 We omit the tables of results, as of no present value. They can be seen in Vail's book, quoted infra.
14 Vail's 'American Electro-Magnetic Telegraph,' Philadelphia, 1845.
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