I have the honor to be, very respectfully, your obedient servant, McCLINTOCK YOUNG, _Secretary of the Treasury ad interim._ Hon. JOHN W. JONES, _Speaker of the House of Representatives._ No. 15. _Letter from Professor Morse to Hon. McClintock Young._ WASHINGTON, _June 3, 1844_. SIR: I have the honour to report that the experimental essay authorized by the act of Congress on March 3d, 1843, appropriating $30,000 for “testing” my “system of electro magnetic telegraphs, and of such length, and between such points, as shall test its _practicability_ and _utility_,” has been made between Washington and Baltimore—a distance of forty miles—connecting the capitol in the former city, with the rail road depot in Pratt street, in the latter city. On the first point proposed to be settled by the experiment—to wit, its _practicability_—it is scarcely necessary to say (since the public demonstration which has been given of its efficacy, for some days past, during the session of the different conventions in the city of Baltimore) that it is fully proved. Items of intelligence of all kinds have been transmitted back and forth, from the simple sending of names, to the more lengthened details of the proceedings of Congress and the conventions. One fact will, perhaps, be sufficient to illustrate the efficiency and speed with which intelligence can be communicated by the telegraph. In the proceedings of the democratic convention at Baltimore for the nomination of a candidate for President of the United States at the next election, the result of the votes in the nomination of the Hon. J. K. Polk was conveyed from the convention to the telegraphic terminus in Baltimore, transmitted to Washington, announced to the hundreds assembled in front of the terminus at the Capitol, and to both Houses of Congress; the reception of the news at Washington was then transmitted to Baltimore, sent to the convention and circulated among its members—all before the nomination of the successful candidate was _officially announced_ by the presiding officer of the convention. In regard to the _utility_ of the telegraph, time alone can determine and develop the whole capacity for good of so perfect a system. In the few days of its infancy, it has already casually shown its usefulness in the relief, in various ways, of the anxieties of thousands; and, when such a sure means of relief is available to the public at large, the amount of its usefulness becomes incalculable. An instance or two will best illustrate this quality of the telegraph: