the railroad leading from Dublin to Dundalk, and this system was at one time so popular, that it was proposed to unite England and France by means of compressed air; but it was found that the variation of the temperature with every stroke of the engine, was so great, as to vary the speed very perceptibly. There was also an atmospheric railroad built in England, which consisted of a tube some three feet in diameter, running the whole length of the road, and laying between the rails; this tube had a slot or opening on the upper part, through which came a projection from the piston, which was fitted to this tube. The cars being attached to this piston, the air is exhausted from one end, which causes a vacuum, the air behind the piston pushes it forward with great velocity; but, owing to a variety of difficulties, this method, I believe, is now entirely abandoned.

The Chairman. This atmospheric railroad differs from the ordinary roads only in its motive power; they had all the other appliances of other railroads, such as double track, cars, &c. Now, when we consider the cost of laying this center tube, and keeping it in repair, it will be found that the usual mode of taking the power along, and using it as it is wanted, is much superior.

Dr. Parmelee. I believe that the time is not far distant, when coal will be dispensed with for generating steam, and that petroleum will take its place. In Pennsylvania, at the oil wells, they use the oil to generate the steam in their boilers, and they find that 500 pounds of petroleum will do as much, in the way of fuel, as 2,000 pounds of coal, thus doing away with 1,500 pounds of coal, which, on cars or steamboats, is of great importance. But the introduction of anything new is always attended with great difficulty; we all know the prejudice there was to the use of the steam fire engine, the obstacles in way of their introduction seemed almost insurmountable, and we all know how valuable they are 'at present. Mr. Godwin read the following statistics of the exports of petroleum from the United States, in first quarter of the year:

Export from New York to foreign ports, from Jan. 1, 1863, to April 6, 1863.

In addition to the above, there has been exported to foreign ports, since 1st January, from Boston, 939,891 gallons; from Philadelphia, 1,377,039, gallons; from Baltimore, 364,806 gallons; and from Portland, 155,463 gallons-total 2,837,199 gallons-making a total export from the United States, since 1st January, of 9,831,717 gallons.

Mr. Page. I believe that the supply of petroleum is like the supply of coal, almost inexhaustible. Canada is full of it, Oregon, Ohio, and California, West Indies, Ceylon. There are, no doubt, millions of gallons lying in the earth, like the gold in California. When the oil was first discovered it had to be pumped up, but nature then came to the assistance of man, and forced it up. Last year petroleum was sold for nine cents a gallon; it is now sixteen. We have lately sent from 3,000 to 4,000 barrels a day to Germany, and it is going to the very place where they have it under their feet. Japan is full of it, and I have been told that they burn it in the streets of Japan by placing the oil in wooden tubes, and then lighting it. The uses to which it can be applied are very numerous, and I should like to see it employed as fuel in steam boilers.

Dr. Rich.-Several years ago I was present when a plan was brought before the American Institute for a railroad in Broadway, to be under the street. The idea was to build a vault under the roadway; the advantages claimed for it were, that it would be out of the way of vehicles, and warm in winter and cool in summer, easy of access at all times, and very dry; it was to be lighted throughout with gas; the speed could also be increased to twice that above ground, and fires would not interfere with their running. The plan appeared to be perfect in every detail.

The Chairman.—I see they have in operation in England, a Yankee invention, called a pneumatic railway, about a mile in length. It is an air gun arranged to carry packages, by discharging them through a pneumatic tube. It is said that the length of this tube, one mile, can be traversed in one minute. Traveling with the wind, neither faster nor slower, nothing is felt of its influence except just a very little when going head foremost, from the air which finds its way in at the end of the tube. The space is too small for reverberation, and there is less noise than would be expected from iron rattling on iron.

"Harbor Defences, and the Use of Iron-clad Vessels," was selected as the subject for discussion for the next meeting. Adjourned.

JOHN W. CHAMBERS, Secretary pro tem.

AMERICAN INSTITUTE POLYTECHNIC ASSOCIATION,

April 23, 1863.

}

The Chairman, S. D. TILLMAN, Esq., presiding.

IMPROVED ROADS.

Mr. J. K. Fisher.-During a residence in Naples, some years ago, I speculated on the subject of lava, as a material for roads. It was used to pave the streets of Pompeii, and is still used in Naples-and seems sufficiently hard for the purpose-much harder than many stones used for paving and road making. And it may be molded into blocks while it is in a semi-fluid state, as it flows for miles, and its surface may be roughened according as the mold is made. A railway might be laid to transport the blocks to the shore, or even to Naples; and vessels may transport them to cities where they are wanted.

After my return, I went with several members of the Institute to see the operation of making plate glass, at Williamsburgh. It struck me that the glass was nearly of the consistency of lava as it flows from Vesuvius, and that, could we make artificial lava, we might roll it into plates as they roll glass; and we might make them thick enough to pave with.

It also occurred to me that a road might in this way be surfaced with cast iron. To do it would require a furnace moving on wheels, at a steady and slow rate; such a rate as would bring the roller into contact with the melted metal upon the road just in time to give it the requred shape and a sufficient chill. And if a great extent of road were to be covered with a continuous sheet of iron, several furnaces might be required, so arranged upon the moving platform as to relieve each other, and to produce a regular flow of metal.

In laying either iron or lava in this way, it appears to me, it is practicable to give any desired roughness to the surface, any figure or pattern that may be best for the foothold of horses. And this roughness may be spread over the whole surface, as in the iron pavement invented by Mr. Tillman, or it may be confined to the horse tracks, leaving the wheel tracks smooth.

In publishing this idea of a traveling furnace to pour melted lava or iron upon the road, and a roller to surface and chill it, I wish it to be understood that I do not abandon my claim to a patent for whatever is original in it. I publish it for the purpose of obtaining aid to determine whether the design is worth pursuing; and, if worth pursuing, to invite the coöperation of engineers and capitalists, and others who may help to promote it. How much of it is new, and how much of it may have been known before, I cannot now say.

It may be objected to this plan, as it was objected to Barlow's continuous rail, that the expansion and contraction due to changes of temperature will work the iron or lava. But in the case of Barlow's rail, and others similar to it, it was found that the elasticity of wrought iron was sufficient to compensate for the effects of temperature; and that, practically, there was little or no difficulty from contraction and expansion, even in split rails, where, at points, only half the section of metal was available to resist the force of contraction. In case of a continuous sheet of cast iron, of even breadth and thickness, or equal cross section, there would be less liability to derangement; because, first, the whole length would stretch to the extent of its elasticity before rupture or permanent set would occur at any point; and, second, because the elasticity of cast iron is greater than that of wrought iron, in the proportion of seven to six. Compared with a line of continuous split rail, like that for a long time used on the New York Central railway, a continuous cast iron road surface would bear a charge of 140 degrees as well as the rails would bear a charge of 60 degrees, or it would bear a charge of 280, degrees as well as the rails would bear 120 degrees. But it is not absolutely required that the road be continuous; there may be slip joints at intervals, if there be much difficulty in making it solid. Even cracks, such as might occur in a road made without skill, would be trifling when compared with the defects of the best pavement we have at present.

If these ideas be correct, it is practicable to pass a movable foundry through a street, upon a temporary railway, leaving behind it a floor of cast iron, either smooth, or indented to prevent slipping, and shaped to secure drainage. I think the whole surface, from house to house, should be made at one operation, and the ups and downs at crossings should be avoided, as they are in Naples, Florence, and other cities that are paved with stones like those of our new sidewalks in Broadway. And access to sewers and pipes should be from the sides, and not down from the surface, as was proposed by the London engineers twenty years ago.

The cost of cast iron paving on this plan would, I believe, be much less than that of cast iron laid in pieces. There would be no displacement, and repairs would not be required, except in cases of breakage, which ought never to occur. And we have had practical proof, from Scotland, that cast iron paving remains apparently uninjured after good stone paving, subject to the same traffic, has become unfit for use; and that the annual cost of the iron is less than half that of the stone. Could we sum up the cost of relaying, incumbering the streets, repairing, cleaning, the waste of motive power, damage to carriages and their loads, wear of shoes, [AM. INS.] 33

and injury from dirt, I believe we should find that the common pavement costs ten times more than the best iron pavement.

But if the best and most agreeable paving were to cost double or treble; if, instead of $1,200,000 per year, which we have in some years paid for paving and cleaning, we were to pay three millions, and be free from dirt, I think the citizens would choose the decent system, and no more desire to resume the indecent one, than they desire to be relieved from the Croton water and the cost of it, or the sewers and their cost.

But if the citizens generally, of all conditions, did wish to endure the present nuisances, rather than pay the taxes necessary to maintain a system accordant with taste and science, it would be the more incumbent on a liberal scientific association to show the desirableness of the better system. It may be the policy of politicians to tell the public only what the public already knows, or is prepared to believe; but men of science, who belong to the liberal professions, must not seek popularity by such means. This I say for the admonition of those who are disinclined to agitate improvements that are not likely to come into use within a short time. Not only in streets, but in suburban thoroughfares, and in all roads of great traffic, would this means of surfacing be applicable. Cast iron would be profitable where the traffic exceeds a certain amount, easily found by calculation. On roads of less traffic, but still considerable, lava would be profitable, as I think. But I do not know the cost of making it; the heat required; the distance from which the materials would have to be brought; these are points upon which I ask for information.

After which the regular subject for the evening, "Harbor Defences, and the Use of Iron-clad Vessels," was taken up, when the Chairman said:

It will be remembered that we had this subject once before under discussion last winter, but since then some new experiments have been made at the South, and the civilized world is anxiously waiting the result of the recent trial at Charleston. As this is the third practical test of iron clad vessels, and some important facts in naval warfare have been determined, the subject has been again selected for discussion.

Mr. Dibben.-The accounts of the late trial at Charleston are so very meager, and so little that is definite known, that we cannot enlarge very much on our previous discussion, and all that I can say I fear will be but a repetition of what has been said before. There is this difference, however, in the late fight, that it was not iron-clads against iron-clads, but forts against iron-clads, and the iron-clads stood it well; from what we have heard, these iron-clads have stood all the battering the forts were capable of giving, without incurring any serious damage. Whether they tried to remove the obstructions in Charleston harbor does not appear; but from what we know we can conclude that the barring up of the entrance to this city at the Narrows, will stop all the iron-clads in the world. We have penetrated seven and eight inches of iron through and through, at a little less distance than this battle was fought. The English and French ron-clads have plates of from four to five inches thick; every shot from our rifle guns would go through these plates, at 400 and 500 yards. I do not think that all the iron-clads in the world would undertake to do what these seven monitors did, to expose them to a fire of 300 heavy guns for over