1869.] on the Mechanical Pro]pe7iies of Steel. 25 



pressure and section. In order to determine the resistance of the 

 bars to a force aualagons to that of impact, the work in deflecting 

 each bar up to its hmit of elasticity has been calculated. These 

 results difl'er considerably from each other, showing the different 

 degrees of hardness, ductility, &c., of the material of which the bars 

 are composed. The transverse strength of the different bars up 

 to their limit of elasticity is shown by the amount of the modulus 

 of strength or the unit of strength calculated for each bar. 



Table II., on Tensile Strain, gives the breaking-strain of each 

 bar per square inch of section, and the corresponding elongation of 

 the bar per unit of length, together with the ultiinate resistance 

 of each bar to a force analogous to that of impact. 



Table III., on Compression, gives the force per square inch of 

 section requisite to crush short columns of the different specimens, 

 with the corresponding compression of the column per unit of 

 length, together with the work expended in producing this com- 

 pression. 



It will be observed from the following Tables that the results of 

 the experiments show that the deflections produced by a transverse 

 strain are in proportion to the pressures within the limits of elas- 

 ticity. 



In Table I., as in the other two on tension and compression, 

 the value of the work done on each specimen has been determined, 

 and the results recorded in the last column indicate the comj^arative 

 strength of each particular bar ; and the mean value of the deflec- 

 tions corresponding to unity of pressure and section will be found 

 in column 3. These may be taken as the measure of flexibility, 

 elasticity, and ductility of the different bars, and the uses to which 

 the material may be applied. 



The mean value of E, the modulus of elasticity taken for thirty 

 of the best specimens, is about 31,000,000, which exceeds that of 

 wrought iron by more than the thhtieth part. Steel having a much 

 greater flexibihty than malleable iron, accounts for the apj)roxima- 

 tion of their respective values in D^. This arises from the fact that 

 the bars of the greatest flexibility — other tlnngs being the same — 

 have the least value for the modulus of elasticity. 



On tensile strain the mean result derived from thirty of the 

 best specimens is 47'7 tons, or nearly 48 tons per square inch; 

 and in this, as in the previous Table, the measure of ductility and 

 strength is given in the last column, Avhich indicates the utility of 

 the material and the purposes for which it may be selected. 



Comparing the best quality of steel with the best wrought 

 iron at 24 tons as the breaking-weight per square inch, we find 

 that we have a material of double the strength with the same 

 weight, or what is the same thing, of only half the weight with the 

 same strength, or as 47*7 to 24. In the art of construction these 



