434 



off and will necessarily vary, and can only be ascertained in each 

 experiment by first establishing the ratio they bear to each other. 

 For this purpose the first ten experiments are used, in all of which 

 the metal was from | to 1 inch in thickness, and its mean tensile 

 strength ascertained by direct experiment to be 18,750 Ibs. per inch. 

 The resulting mean value of is= 16,573 Ibs., and the ratio of/ to f 

 as 1 to -847. 



By using results obtained by Prof. Hodgkinson on the breaking 

 weight of inch bars of ten different descriptions of iron, where the 

 tensile strength was ascertained by direct experiment, it would ap- 

 pear that the ratio between the resistance of tension and the resist- 

 ance of flexure varies in different qualities of metal, an inference 

 which seems to be confirmed by other experiments on rectangular 

 bars given in the Report of the Commissioners on the application of 

 iron to railway structures. The mean result, however, accords 

 nearly with that of the author's experiments, and gives the ratio of 

 f to $ as 1 to *853. Hence, according to these data, the resistance 

 to flexure, computed as a force evenly distributed over the section, 

 is almost nine-tenths of the tensile resistance. 



This ratio of the values of/ and being applied to the equations 

 resulting from the several experiments, gives the tensile strength of 

 the metal as derived from each form of section, and the results, 

 though not perfectly regular, are found to be within the limits of 

 the variation exhibited by the metal as shown by the experiments 

 on direct tension in the former paper. Classified and condensed, 

 these results are as follows : 



The mean tensile strength as obtained from 



The open girders, is 18,282 



The solid rectangular bar of 2 inches sectional area 17,971 

 The inch bars square and round, and square broken 



diagonally 19,616 



The bars of 4 inches sectional area, square and 



round, and square broken diagonally 16,800 



The compound sections in which the metal was 



i inch thick 19,701 



Having thus found that his formulae, when applied to his own 

 experiments, gave consistent and satisfactory results, the author next 



