It is obvious that, amongst the conditions of machinery for accomplishing such an object, it would be desirable to reduce the weight of matter to be conveyed along with the letters: it would also be desirable to reduce the velocity of the animal power employed; because the faster a horse is driven, the less weight he can draw. Amongst the variety of contrivances which might be imagined for this purpose, we will mention one, which, although by no means free from objections, fulfils some of the prescribed conditions; and it is not a purely theoretical speculation, since some few experiments have been made upon it, though on an extremely limited scale. 336. Let us imagine a series of high pillars erected at frequent intervals, perhaps every hundred feet, and as nearly as possible in a straight line between two post towns. An iron or steel wire must be stretched over proper supports, fixed on each of these pillars, and terminating at the end of every three or five miles, as may be found expedient, in a very strong support, by which it may be stretched. At each of these latter points a man ought to reside in a small stationhouse. A narrow cylindrical tin case, to contain the letters, might be suspended by two wheels rolling upon this wire; the cases being so constructed as to enable the wheels to pass unimpeded by the fixed supports of the wire. An endless wire of much smaller size must pass over two drums, one at each end of the station. This wire should be supported on rollers, fixed to the supports of the great wire, and at a short distance below it. There would thus be two branches of the smaller wire always accompanying the larger one; and the attendant at either station, by turning the drum, might cause them to move with great velocity in opposite directions. In order to convey the cylinder which contains the letters, it would only be necessary to attach it by a string, or by a catch, to either of the branches of the endless wire. Thus it would be conveyed speedily to the next station, where it would be removed by the attendant to the commencement of the next wire, and so forwarded. It is unnecessary to enter into the details which this, or any similar plan, would require. The difficulties are obvious; but if these could be overcome, it would present many advantages besides velocity; for if an attendant resided at each station, the additional expense of having two or three deliveries of letters every day, and even of sending expresses at any moment, would be comparatively trifling; nor is it impossible that the stretched wire might itself be available for a species of telegraphic communication yet more rapid.