108 REPORT—1846. 
the bottom, in a rectangular tube, should be as 5 to 3. These proportions were de- 
duced from the experiments on the smaller description of tubes, or those having the 
corrugated top, and thick plates on the upper sides. The plates forming the top of 
the model tube were rather thicker than intended, and consequently gave (according 
to the former experiments) a preponderating power of resistance to that part. To 
obviate this disparity, two additional strips, 61 in. by 5-16ths in, thick, about 4 cwt., 
were riveted along the bottom to an extent of 20 ft. on each side of the shackle. This 
increase raised the area of the bottom to nearly thirteen inches, being about the ratio 
of 5 to 8 or 23°5 to 13. With these proportions, and having repaired the fractured 
part by the introduction of some new plates, the experiment proceeded as before, 
Second experiment. Breaking weight, 97,102 lbs.=43-3 tons.— Ultimate deflection, 
4*11 inches.—Permanent set could not be taken. In this experiment the tube failed, 
by one of the ends giving way, which caused the sides to collapse. The weak point 
in this experiment was evidently a want of stiffness in the sides. To remedy this 
evil, and keep them in form, a number of vertical ribs, composed of light angle iron, 
were riveted along the interior of each side, at distances of 2 ft.; and having again 
restored the injured parts, the tube was a third time subjected to the usual tests. 
Third experiment. Breaking weight, 126,138lbs.—56°3 tons.— Ultimate deflection, 
5-68 inches.—Permanent set, or defects of elasticity=1'96 in. After suspending a 
weight of 12],443 lbs., the platform unfortunately gave way, causing an interruption 
to the experiment. This was, however, speedily repaired, and the experiment con- 
tinued, when the tube was ultimately torn asunder, through the bottom plates, by 
a weight of 126,138 lbs. The above experiment was one of the most satisfactory 
description, as, at the moment of fracture, the cellular top gave evident symptoms 
of yielding to a crushing force, by the puckerings of each side, which were gra- 
dually enlarged as the deflection increased. These appearances became more ap- 
parent as the joints of the plates on the top side had cut a number of the rivets 
in two, and the holes had slid over each other to an extent of nearly 3-10ths of 
an inch, ‘The conclusive nature of the whole of the experiments on the model 
tube is highly satisfactory: they exhibit extraordinary powers of resistance; and 
considering that the weight of the whole material contained in the tube does not 
exceed 5 tons; that the distance between the supports is 75 ft.; and the load in 
the middle |1 times its own weight, or 22 times if equally distributed, it is probably 
not over-rating its powers to state that hollow beams of wrought iron, constructed on 
this principle, will be found (whether used for bridges or for buildings) about three 
times stronger than any other description of girders. 
Experiments on the Tubular Bridge proposed by Mr. Stephenson for cross- 
ing the Menai Straits. By E. Hopexiyson, F.R.S. 
Finding that a number of experiments had been made upon cylindrical and ellip- 
tical tubes, and a few upon rectangular ones, Mr. Hodgkinson expressed a con- 
viction that the tubes then tried and others proposed, would not be the best for the 
intended purpose, though they would afford valuable introductory knowledge. He 
urged that the tube, to bear the greatest weight, must be formed as a large beam 
or girder, having its top and bottom equally capable of resistance, and with sides 
strong and stiff enough to keep them at their proper distance; and as it was 
found that the tube usually gave way at the top by buckling, and hence would 
require additional metal, and might perhaps be very heavy, he suggested that 
the top should be formed of cylindrical tubes, as he felt that these tubes, or some- 
thing analogous to them, would best resist the strain to which the top would be 
exposed. The following are some of the leading results; and, first, those from 
the fracture of two similar tubes, as in the following table :— 
Length | Weight |Distance| Depth | Breadth ; Breakin 
of of |between| of of eee mneial weight 
Tube. | Tube, |supports.| Tube. | Tube. | ? SOF att neh. | sta wanes 
ft. in. cwt. qr. it, ft. ft, in. Top. Bottom, Side. “ 
Skee GO ea Vas 2 1 4/6 4 2) 261 
47 OL OF SPOS 2° OT 9 6 “SY GBS 
