But it is a well-established fact, that, as facilities of intercourse increase between different parts of the country, the greater is that intercourse. Thousands travel, in this day of rail roads and steamboats, who never thought of leaving their homes before. Establish, then, the means of instantaneous communication between the most distant places, and the telegraphic line of a single circuit will very soon be insufficient to supply the demands of the public—they will require more. Two circuits will of course _double the facilities, and double the revenue_; but it is an important fact, that the expense of afterwards establishing a second, or any number of circuits, does not proceed on the _doubling_ principle. If a channel for conveying a single circuit be made, in the first instance, of sufficient capacity to contain many more circuits, which can easily be done, additional circuits can be laid as fast as they are called for, at but little more than the cost of the prepared wire. The recent discovery of Professor Fisher and myself, shows that a single wire may be made the common conductor for at least six circuits. How many more we have not yet ascertained. So that, to add another circuit is but to add another wire. Fifty dollars per mile under these circumstances, would therefore add the means of doubling the facilities and the revenue. Between New York and Philadelphia, for example, the whole cost of laying such an additional circuit would be but $5,000, which would be more than defrayed by _two months’_ receipts only from the telegraphs between those two cities. There are two modes of establishing the line of conductors. The first and cheapest is doubtless that of erecting spars about 30 feet in height and 350 feet apart, extending the conductors along the tops of the spars. This method has some obvious disadvantages. The expense would be from $350 to 400 per mile. The second method is that of enclosing the conductors in leaden tubes, and laying them in the earth. I have made the following estimate of the cost of this method: Wire, prepared, per mile, $ 150.00 Lead pipe, with solderings, 250.00 Delivery of the pipe and wire, 25.00 Passing wire into the pipes, 5.00 Excavations and filling in about 1,000 yards per mile, or 3 feet deep, at 15 cents per square yard, 150.00 Laying down the pipe, 3.00 —————— 583.00 ======