418 Notices respecting New Books. 



is secured by having the material in the section accumulated, as far 

 as practicable, at the greatest distances from the neutral axis ; and 

 as regards the cellular structure in the French invention especially, 

 Grubenmann erected a bridge at Wettingen about the middle of the 

 last century, in which the timbers composing the roof of the bridge 

 were made to form the material resisting the force of compression. 

 We shall now proceed to show, that the manner in which these prin- 

 ciples are employed in the English and French inventions is, in cer- 

 tain respects, so decidedly different, as to lead us to regard them as 

 independent discoveries. 



1 . The inventions tvere independent in their origin. — The English en- 

 gineers sought to determine the best form of a tube for resisting trans- 

 verse strain, composed of sheet iron. Dr. Guyot formed the conception 

 of an arched bridge constructed of iron bars. Mr. Fairbairn, by a series 

 of the most elaborate experiments perhaps ever made on the strength 

 of materials, discovered by induction the best form of these tubes. On 

 the contrary. Dr. Guyot, by a combination of principles already 

 known, and without any preliminary experiments, seems at once to 

 have constructed his model. It will be instructive, as well as bearing 

 upon the controversy, to trace the origin of the cellular structure in 

 the English tubular beams. It was not derived from abstract rea- 

 soning ; on the contrary, it was entirely due to the results of experi- 

 ment : after Mr. Fairbairn had experimented upon the cylindrical, 

 elliptical, and rectangular beams having a uniform thickness, he 

 observed that the thin plates on the upper side invariably crumpled 

 up from the force of compression ; he then hit upon the fortunate 

 conception of bending a piece of sheet iron over that part, thereby 

 forming a cell, or, as he called it, a fin, at the upper side of the tube ; 

 the experiments showed that this mode of construction gave a con- 

 siderable additional strength to the beam. This principle was next 

 combined with the rectangular form, and a model rectangular beam 

 with a cellular corrugated top was constructed ; and the experiments 

 on this beam showed that this form of construction gave nearly 

 double the strength of the cylindrical or elliptical forms when com- 

 posed of plates of uniform thickness. Finally, on account of sim- 

 plicity of construction, the model beam of the Conway Bridge was 

 made with rectangular cells at the top to resist the crushing force, 

 and with simple plates at the bottom to resist the force of extension. 

 It is therefore not true, as Dr. Guyot insinuates in his letter to 

 Monsieur Maire, that the plan of the Conway model tube was formed 

 suddenly and without any previous recognition of principles. It 

 may be further worthy of observation, that Mr. Fairbairn never heard 

 of Dr. Guyot's model bridge until very recently. 



2. Ihe two modes of construction differ in their general form. — The 

 Conway and Menai bridges are straight tubes, or at least practically 

 so, composed of sheet iron connected together by rivets and angle- 

 irons, through which railway trains pass. On tiie other hand. Dr. 

 Guyot's model is an arched bridge, composed of iron bars chiefly 

 bolted together, over the top of which the line of railway is supposed 

 to pass. In the English invention, the cells are composed of conii- 



