435 



tested them by other known experiments, and especially refers to 

 those by Major Wade on the transverse strength of square and round 

 bars of cast iron of different qualities, related in the " Reports on 

 the Strength and other Properties of Metals for Cannon," presented 

 to the United States Government by the Officers of the Ordnance 

 Department. The unit of strength, as computed by Major Wade 

 from these experiments, came out uniformly much higher in the 

 round than in the square bars of the same kind of iron, whence he 

 was led to doubt the correctness of the formula employed ; but the 

 author shows that when his formula is used, which includes the re- 

 sistance of flexure, the discrepancy referred to disappears, and the 

 tensile resistance, whether obtained for the round or the square bars, 

 agrees very nearly with that derived from the experiments on direct 

 tension under like circumstances. 



As to the ratio between the resistance of flexure and the tensile 

 resistance, it is remarked that, were the metal homogeneous, the 

 former resistance would probably be precisely equal to the latter, in- 

 stead of bearing the ratio of nine-tenths, as found by experiment ; but 

 the ratio evidently varies in different qualities of metal ; and accord- 

 ingly from Major Wade's experiments, it appears that with the same 

 metal subjected to different modes of casting, an increase of trans- 

 verse strength may accompany a decrease in the tensile resistance. 



Respecting the limit of action of the resistance of flexure, the 

 author observes, that in all the simple solid sections, the- points of 

 action are evidently the centres of gravity of the half- section ; while 

 in the compound sections it is necessary to compute the centre rib and 

 flanges as for two separate beams in which the resistance of flexure 

 is different, and has its point of action at the centre of gravity of the 

 separate portions. It would appear that the elastic reaction deve- 

 lopes this resistance to the full extent when the section is such that 

 a straight line may be drawn from every point at the outer portion 

 to every point at the neutral axis within the section ; but that if 

 the form of section is such that straight lines drawn from the outer 

 fibres or particles to the neutral axis fall without the section, then it 

 must be treated as two separate beams, each having that amount of 

 resistance of flexure due to the depth of the metal contained in it. 



The last section of the paper is devoted to the consideration of 

 the resistance of flexure in wrought iron ; and experiments are first 



