iO^ Analysis of Scientific Books. 



inches; aud the distance between the supports 24 inches. It 

 was soft, so as to yield easily to the file. 



With a load of 18.6 lbs. the depression in the middle was 0.05 in. 



37.0 0.10 „ 



47.0 0.127,, 



The bar was then hardened, so that a file made no impression on 

 any part of it, and the same loads did not produce flexures that 

 were sensibly different from those in the soft state. 



The temper was then lowered till it assumed an uniform straw 

 colour ; when with a load of 



47lbs. the depression in the middle was 0.127 inches. 



85 0.230 „ 



130 0.350 „ 



150 0.400 „ 



The load of 150lbs. produced a permanent set of 0.012, but ISOlbs- 



produced no sensible effect. The loading was continued, and with 



185lbs. the depression in the middle was 0.50 inches, 



385 1.04 „ 



When 385lbs. had been upon the bar about a minute, it emitted a 

 faint creaking sound, and consequently no more weight was added ; 

 in about fourteen minutes the bar broke, exactly in the middle of 

 the length. 



On comparing the fractures of the specimens, there was no ap- 

 parent difference except in colour. The grain was fine, and equal ; 

 the small sparkles of metallic lustre abundant, and equally dif- 

 fused ; but in the harder specimen they had a whiter ground. 



From these experiments it appears that the elastic force of steel 

 is sensibly the same in all states of temper. 



The height of the modulus of elasticity, calculated by the for- 

 mula given by Dr. Young in his Nat. Phil. (Vol. II. p. 48,) is, 

 according to the first experiment, .... 8,827,300 feet. 

 And according to the second experiment . . 8,810,000 feet. 



Now the height of the modulus, as has been determined by Dr. 

 Young for steel by experiments on vibration, is 8,530,000 feet. 

 (Nat. Phil. II. p. 86.) The modulus for cast steel calculated from 

 Duleau's experiments {Essai Theoriqiie et Experimental sur le Fer 

 ForgCi p. 38,) is 9,400,000 feet, and for German steel 6,600,000 

 feet. 



The force which produces permanent alteration is, to that which 

 causes fracture in hard steel, as 350 : 580; or as 1 : 1.66 ; in the 

 same steel of a straw-yellow temper as 150 : 385, or as 1 : 2.56. 



When the tension of the superficial particles at the strain which 

 causes permanent alteration, is calculated by the formula given in 

 Mr. Tredgold's Essa7j on the Strength of Iron^ p. 146, Second Edi- 

 tion, it is 45,000lbs. upon a square inch in tempered steel ; and 

 the absolute cohesion 115,000lbs. Mr. Rennie found the direct 



