TO A FRIEND IN PHILADELPHIA.

Paris, March 16, 1789.

I LEAVE this place to-morrow for London: I go expressly for the purpose of erecting an iron bridge, which Messrs. Walkers, of Rotheram, Yorkshire, and I have constructed, and is now ready for putting together. It is an arch of one hundred and ten feet span, and five feet high, from the chord line. It is as portable as common bars of iron, aud can be put up and taken down at pleasure, and is, in fact, rendering bridges a portable manufacture.

With respect to the French revolution, be assured that every thing is going on right. Little inconveniencies, the necessary consequences of pulling down and building up, may arise; but even these are much less than ought to have been expected. Our friend, the Marquis, is like his patron and master, General Washington, acting a great part. I take over with me to London the key of the Bastile, which the Marquis intrusts to my care as his present to General Washington, and which I shall send by the first American vessel to New York. It will be yet some months before the new Constitution will be completed, at which time there is to be a procession, and I am engaged to return to Paris to carry the American flag.

In England the ministerial party oppose every iota of reformation: the high beneficed clergy and bishops cry out that the church is in danger; and all those who were interested in the remains of the feudal system join in the clamour. I see very clearly that the conduct of the British government, by opposing reformation, will detach great numbers from the political interests of that country; and that France, though the influence of principles and the divine right of men to freedom, will have a stronger party in England than she ever had through the Jacobite bugbear of the divine right of kings in the Stuart line.

I wish most anxiously to see my much loved America. It is the country from whence ali reformation must originally spring. I despair of seeing an abolition of the infernal traffic in negroes. We must push that matter further on your side of the water. I wish that a few well instructed could be sent among their brethren in bondage; for until they are enabled to take their own part, nothing will be done. 1 am,

With many wishes for your happiness,
Your affectionate friend,

THOMAS PAINE.

TO SIR GEORGE STAUNTON, BART.

SIR,

As I know you interest yourself in the success of the useful arts, and are a member of the society for the promotion thereof, I do myself the pleasure to send you an account of a small experiment I have been making at Messrs. Walkers' iron works at this place. You have already seen the model I constructed for a bridge of a single arch to be made of iron, and erected over the river Schuylkill, at Philadelphia; but as the dimensions may have escaped your recollections, I will begin with stating those particulars.

The vast quantities of ice and melted snow at the breaking up of the frost in that part of America, render it impracticable to erect a bridge on piers. The river can conveniently be contracted to four hundred feet, the model, therefore, is for an arch of four hundred feet span; the height of the arch in the centre, from the chord thereof, is to be about twenty feet, and to be brought off on the top, so as to make the ascent about one foot in eighteen or twenty.

The judgment of the Academy of Sciences at Paris has been given on the principles and practicability of the construction. The original, signed by the Academy, is in my possession; and in which they fully approve and support the design. They introduce their opinion by saying,

"Il est sur que lors qu'on pense au projet d'une arche en fer de 400 pieds d'overture, et aux effets qui peuvent resulter d'une arche d'une si vaste étendue, il est difficile de ne pas élever des doutes sur le succès d'une pareille enterprise, par les difficultés qu'elle presente au prémieré apperçu. Mais si telle est la disposition des parties, et la manière dont elles sont reunis qu'il result de cet assemblage un tout trés ferme et trés solide, alors on n'aura plus les memes doutes sur la reussite de ce projet."*

*It is certain that when such a project as that of making an iron arch of four hundred feet span is thought of, and when we consider the effects resulting from an arch of such vast magnitude, it would be strange if doubts were not raised as to the success of

The Academy then proceed to state the reasons on which their judgment is founded, and conclude with saying,

"Nous concluons de tout ce que nous venons d'exposer que la pont de fer de M. Paine est ingenieusement imaginé, que la construction en est simple, solide, et propre à lui donner la force necessaire pour résister aux effets resultans de sa charge, et qu'il merite qu'on en tente l'execution. Enfin, qu'il pourra fournira un nouvel exemple de l'application d'un métal dont on n'a pas jusqu' ici fait assez d'usage en grand, quoique dans nombre d'occasions il est peut être employé avec plus grand succès."*

As it was my design to pass some time in England before I returned to America, I employed part of it in making the small essay I am now to inform you of.

My intention, when I came to the iron works, was to raise an arch of at least two hundred feet span, but as it was late in the fall of last year, the season was too far advanced to work out of doors, and an arch of that extent too great to be worked within doors, and as I was unwilling to lose time, I moderated my ambition with a little common sense, and began with such an arch as could be compassed within some of the buildings belonging to the works. As the construction of the American arch admits, in practice, of any species of curve with equal facility, I set off in preference to all others, a catenarian arch of ninety feet span, and five feet high. Were this arch converted into an arch of a circle, the diameter of its circle would be four hundred and ten feet. From the ordinates of the arch taken from the wall where the arch was struck, I produced a similar arch on the floor whereon the work was to be fitted and framed, and there was something so apparently just when the work was set out, that the looking at it promised success.

such an enterprize, from the difficulties which at first sight present themselves. But if such be the disposition of the various parts, and the method of uniting them, that the collective body should present a whole both firm and solid, we should then no longer have the same doubts of the success of the plan.

* We conclude from what we have just remarked that Mr. Paine's Plan of an Iron Bridge is ingeniously imagined, that the construction of it is simple, solid, and proper to give it the necessary strength for resisting the effects resulting from its burden, and that it is deserving of a trial. In short, it may furnish a new example of the application of a metal which has not hitherto been used in any works on an extensive scale, although on many occasions it is employed with the greatest success.

You will recollect that the model is composed of four parallel arched ribs, and as the number of ribs may be increased at pleasure to any breadth an arch sufficient for a road-way may require, and the arches to any number the breadth of a river may require, the constructing of one rib would determine for the whole; because if one rib succeeded, all the rest of the work, to any extent, is a repetition.

In less time than I expected, and before the winter set in, I had fitted and framed the arch, or properly the rib, completely together on the floor; it was then taken in pieces and stowed away during the winter, in a corner of a workshop, used in the mean time by the carpenters, where it occupied so small a compass as to be hid among the shavings, and though the extent of it is ninety feet, the depth of the arch at the centre two feet nine inches, and the depth at the branches six feet, the whole of it might, when in pieces, be put in an ordinary stage waggon, and sent to any part of England.

I returned to the works in April, and began to prepare for erecting; we chose a situation between a steel furnace and a workshop, which served for butments. The distance between those buildings was about four feet more than the span of the arch, which we filled up with chumps of wood at each end. I mention this as I shall have occasion to refer to it hereafter.

We soon ran up a centre to turn the arch upon, and began our erections. Every part fitted to a mathematical exactness; the raising an arch of this construction is different to the method of raising a stone arch. In a stone arch they begin at the bottom, on the extremities of the arch, and work upwards, meeting at the crown. In this we began at the crown, by a line perpendicular thereto, and worked downward each way. It differs likewise in another respect. A stone arch is raised by sections of the curve, each stone being so, and this by concentric curves. The effect likewise of the arch upon the centre is different, for as stone arches sometimes break down the centre by their weight, this, on the contrary, grew lighter on the centre as the arch increased in thickness, so much so, that before the arch was completely finished, it rose itself off the centre the full thickness of the blade of a knife from one butment to the other, and is, I suppose, the first arch of ninety feet span that ever struck itself.

I have already mentioned that the spaces between the ends of the arches and the butments were filled up with

chumps of wood, and those rather in a damp state; and though we rammed them as close as we could, we could not ram them so close as their drying, and the weight of the arch, or rib, especially when loaded, would be capable of doing; and we had now to observe the effects which the yielding and pressing up of the wood, and which corresponds to the giving way of the butments, so generally fatal to stone arches, would have upon this.

We loaded the rib with six tons of pig iron, beginning at the centre, and proceeding both ways, which is twice the weight of the iron in the rib, as I shall hereafter more particularly mention. This had not the least visible effect on the strength of the arch, but it pressed the wood home, so as to gain in three or four days, together with the drying and shrinking of the wood, above a quarter of an inch at each end, and consequently the chord or span of the arch was lengthened above half an inch. As this lengthening was more than double the feather of the key-stone in a stone arch of these dimensions, such an alteration at the butment would have endangered the safety of a stoue arch, while it produced on this no other than the proper mathematical effect. To evidence this, I had recourse to the cord still swinging on the wall from which the curve of the arch was taken. I set the cord to ninety feet span, and five feet for the height of the arch, and marked the curve on the wall. I then removed the ends of the cords horizontally something more than a quarter of an inch at each end. The cord should then describe the exact catenarian curve which the rib had assumed by the same lengthening at the butments; that is, the rising of the cord should exactly correspond to the lowering of the arch, which it did through all their corresponding ordinates. The cord had risen something more than two inches at the centre, diminishing to nothing each way, and the arch had descended the same quantity, and in the same proportion. I much doubt whether a stone arch, could it be constructed as flat as this, could sustain such an alteration; and, on the contrary, I see no reason to doubt but an arch on this construction and dimensions, or corresponding thereto, might be let down to half its height, or as far as it would descend, with safety. I say, "as far as it would descend," because the construction renders it exceedingly probable that there is a point beyond which it would not descend, but retain itself independent of butments; but this cannot be explained but by a sight of the arch itself.