Vol. lxxxv.] philosophical transactions. 5yg 



In this operation we slackened only one of the cords at a time, the rest being 

 sufficient to keep the whole up. The beams were now again separated, and the 

 cramping hooks by the crossing of the cords drew the 1 sides of the sheets 

 together. When all this was properly arranged, and the arches lowered, the 2 

 sides of the sheet were gradually brought to take hold of each other. As we 

 proceeded, the wedges within the arches were forced in successively, till at last, 

 with much care and considerable difficulty, the 1 sides completely embraced each 

 other, and were kept stretched by the swelled inside arches. 



Another circular arch, closed in with boards all around, well rounded off, 

 and only about 2 feet 3 inches long, had a vacancy at the top into which we 

 could introduce the iron seaming bars for indenting, and for closing up the long 

 seam of the 2 sides. This arch also had its stretchers for swelling it up, and 

 served at the same time, as soon as the seam was properly closed, to beat with 

 mallets the whole sheet all around on its well-finished outside, in order to take 

 away any accidental bulge which it might have received in the long preparations 

 it had undergone, till it came to the present state. The same arch, as soon 

 any portion of the tube had been done, was removed to another place, and the 

 whole was by this means completely seamed up. The theory on which the 

 strength of so thin a cylinder of iron is founded, is, that the sides of it must 

 unavoidably support it, provided you can secure the cylindrical form of the tube. 

 It appeared to me the most practical way to obtain this end by the following con- 

 trivance. By a few experiments I found that a slip of sheet iron, a little thicker 

 than that of the tube, and doubled to an angle of about 40 degrees, might 

 afterwards be made circular. The deepest we could conveniently bend, and such 

 as I supposed would answer the end, was when the sides were about 2i inches 

 broad. They were shaped red-hot on a concave tool, which had the required 

 curvature and angle of the slips. The pieces were long enough to form a complete 

 quadrant of the circle, with the ends sufficiently projecting to be seamed 

 together. 



Before they were joined the sides received another bending, which was given 

 them by tools of a proper convexity. A back was next prepared, consisting of 

 a slip of iron turned up at both sides, and also bent to the circle. Last of all 

 the 4 quadrants having been put together, and a back put round them, the 

 whole was firmly seamed together, so as to resemble a hollow triangular bar made 

 into a hoop or ring, of a proper diameter to go closely into the tube, so as to 

 keep it extended, and braced to the cylindrical form. One of these rings was put 

 into the middle of every one of the small sheets, which brought them to about 

 23 inches from each other. They were carried in edgeways, and afterwards 

 turned about and forced into their respective places. In order to get them in 

 as they were all obliged to go in from one side, there was substituted, instead of 



