In the construction of this _first line of conductors_, it was necessary that experiments should be made to ascertain the best mode of establishing them. The plan I first suggested in my letter to the Secretary of the Treasury in 1837, (see the House report, No. 6, April 6, 1838,) of placing my conductors upon posts thirty feet high, and some three hundred feet apart, is, after experiment, proved to be the most eligible. The objection, so strongly urged in the outset, that, by being exposed above ground, the conductors were in danger from evil disposed persons, had such weight with me, in the absence of experience on the subject, as early to turn my whole attention to the practicability of placing my conductors in tubes beneath the earth, as the best means of safety. The adoption of this latter mode, for some thirteen miles in England, by the projectors of the English telegraph, confirmed me in the belief that this would be best. I was thus led to contract for lead pipe sufficient to contain my conductors through the whole route. Experience, however, has shown that this mode is attended with disadvantages far outweighing any advantages from its fancied security beneath the ground. If apparently more secure, an injury once sustained is much more difficult of access, and of repair; while upon posts, if injury is sustained, it is at once seen, and can be repaired, ordinarily almost without cost. But the great advantage of the mode on posts over that beneath the ground, is the cheapness of its construction. This will be manifest from the following comparative estimate of the two modes in England and in America: _Cost of English Telegraph._ In pipe, _£_287 6_s._, or $1,275 per mile. On posts, _£_149 5_s._, or $662 per mile. _Cost of American Telegraph, as estimated in House Report, No. 17, 27th Congress, 3d session._ In pipe, $583 per mile. On posts, from $350 to $400 per mile. These comparisons also show how much less is the cost of the American telegraph, even at the highest estimate. But these estimates of the cost of construction, largely exceed the actual cost, under the improved modes recently suggested by experiment, and now adopted; and the cost of the line between Baltimore and Washington, already constructed, involves numerous expenditures of an experimental character, which will not be incident to an extension of the line onward to New York, if that shall be deemed desirable.