Coox.—On the Construction of the Brunner Gorge Bridge. 911 
July last, but to call attention to the most noticeable peculiarity in its con- 
struction, and to investigate mathematieally the tension on the wire ropes 
which supported the bridge. In order, however, to make the calculations 
and other remarks intelligible, it will be desirable to give a short deserip- 
tion of the principal points connected with the structure. And here it will 
be well to state that this information has been derived partly from the 
Report, recently submitted to the General Assembly, of the Commissioners 
appointed to inquire into the cause of the accident; partly from direct 
communications from J. E. FitzGerald, Esq., who was a member of the 
Commission. 
The floor of the bridge was eight feet wide, and on each of its sides it 
was connected by means of suspending rods with a strong wire rope, or 
chain, which passed over two piers, each 25 feet high, one on each side of 
the river ; each end of the chain was connected with an anchor-plate of 
cast iron attached to solid masonry, and intended to be built up with a 
mass of conerete. I may remark, in passing, that delay in executing this 
intention was, in the opinion of the Commission, the principal cause of the 
accident. The distance between the two piers over which the same chain 
passed was 300 feet; the distance between the two piers on the same side 
of the river was 30 feet. This width being much greater than the width of 
the floor of the bridge, 8 feet, it will be seen at once that the chains did not 
hang in a vertical plane. The lowest points of each chain may, it would 
seem, be taken to have touched the floor. None of the suspending rods on 
each side of that central point were vertical; the nearer the rods were to 
the banks of the river, the more and more did they slope outwards, till the 
the pair next the piers must have had their upper extremities nearly as far 
apart as the piers themselves, viz., 80 feet, whilst their lower ones were 
only eight feet apart. It is this peculiarity of construction which it is my 
purpose to examine mathematically, with a view of comparing the tension 
on the chain in this case with what it would have been had the usual 
method of construction been adopted, viz., that in which each chain as well 
as the suspending rods connected with it lie in a vertical plane, passing 
through a pair of piers. The object of this construction was, I believe, to 
stiffen the bridge. 
The bridge was intended to carry, at any one time, only a single truck 
loaded with coals, and never to have a locomotive uponit. It was estimated, 
therefore, that the load, in addition to that caused by the weight of the 
bridge itself, would not exceed ten tons. The weight of the bridge and 
suspending rods appears to have been 82 tons; the weight of each chain, 
seven tons ; so that the total weight under which the bridge gave way was 
only 96 tons, no extra load being on it at the time. 
