10 



buckling of rods. According to these, as is well known, the critical pressure for 

 a rod of slenderness ratio r/1 is determined by means of two constants c and K by 

 the formula 



k = K(1 - c 1/r) (14) 



where for mild steel K = 3100 kg/cm 2 (44,000 lb. per sq. in.) and c = 0.00368. 



FIG. 4. GRAPH FOR DETERMINATION OF BUCKLING PRESSURE. 



One might so interpret Eq. (14), as if in place of the actual elastic 

 modulus, E, the expression 



E - *V^ • (15) 



