ON THE ENDURANCE OF METALS. 



437 



sketch ; the stress being applied by opening and closing the legs of the 

 longs, and thus putting the metal into alternate tension and compression. 

 In the second group, the spring bars and specimens were all sawn and 



Fig. 1. 



Fig. 3. 



1 



T 



t 



slotted out of one piece of steel, and the necessity of constantly tightening 

 up the nuts was thus avoided. In the third, the specimens were shaped 

 as shown by fig. 3, and a bending stress was applied at the centre of the 

 bars. 



Series No. 3. 

 Siift Steel 



Series No. 4. 

 The opportunity afforded by the large use of special plant and 

 machinery at the Forth Bridge Works has been taken advantage of to 

 note the influence of varying stresses on full-sized riveted steel girders. 

 These observations are still in progress, and can be but very briefly referred 

 to herein. In one instance the lever of a large plate-bending press is of box- 

 girder section, built vip of eight 4" X 4" x |" angle bars, two 13" X |" 

 web plates, and two 17" x V' flanges. The span is 15 feet 8 inches, 

 and the ordinary daily working stress on the metal is 43,000 lbs., and 

 occasionally 57,000 lbs. per square inch, the breaking strength being 

 70,000 lbs. Many thousand applications of this stress have been made, and 



