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OBSERVATIONS RELATIVE TO

the adoption of a wrought iron tube is the most efficient, as wellas the most economical, description of structure that can be de-vised for a railway bridge across the Menai Straits.”

Mr. Stephenson then goes on to explain the nature of the ex-periments, admitting the anomalous character of the results ofsome and the efficiency of others, and concludes this part of hisreport by stating, that “ another instructive lesson which theexperiments have disclosed is, that the rectangular tube is byfar the strongest, and that the circular and elliptical should bediscarded altogether.”

Mr. Stephenson next takes a view of the formula obtained byMr. Hodgkinson for the large rectangular tube, which indicatesa breaking weight of 1100 tons, when the plates are assumed tobe 1 inch thick. Now these calculations, however interestingin a scientific point of view, were of no use as regards the con-struction of the Menai Bridge; inasmuch as the rectangulartubes, which I had proposed, having a far more economical dis-tribution of the material, are considerably stronger than thoseto which Mr. Hodgkinson’s formula applies.

From the theoretical investigation of the ultimate strength oftubes, Mr. Stephenson proceeds at once to discuss the merits ofmy report, wherein it is stated, that the tube “ should be ahuge sheet-iron hollow girder, of sufficient strength and stiff-ness to sustain those weights (about 2000 tons); and, pro-vided the parts are well-proportioned, and the plates properlyriveted, you may strip off the chains, and leave it as a usefulmonument of the enterprise and energy of the age in which itwas constructed .” To these views Mr. Stephenson does notappear fully to subscribe, nor did he do so for some monthsafterwards. At the close of his report, he merely adduces someexamples of the danger attending the use of chains, in theordinary form of suspension bridges, and concludes with acautious reservation of opinion as to the adoption or rejection ofsuch auxiliary means of support.