RESISTANCE OK MATKHIALS. 



RESPIRATOR. 



when the wtion is square, i = , 



^ r the radiu* of the solid cylinder : k and A the sides of the 



rectangle, and o the aide of the square ; when the section is annular, 

 calling the external and internal radii respectively r and r', the value 



II a 5 . In practice, the angle of torsion is usually 



( = 0-0005-L, In which n = the distance from the axis to the 



most distant. fibre from itself. Mr. Bevan I' Fhilos. Trans.,' 1829) has 

 . table of the modulus of torsion for the different kinds of wood, 

 which is appended ; and he also states that for metals the modulus of 

 torsion U equal to ^ of the modulus of elasticity. 



Dttnuio*. The resistance to detnision is at times called into 

 action, in timber or iron construction ; and therefore requires to be 

 noticed. It has not been made the subject of any direct experiment >, 

 i supposed in fir timber to be equal to 592 Ibs. per square inch 

 in the direction of the force ; hi cast iron, 73,000 Ibs. ; and in wrought 

 iron, friM 45,000 to 53,000 Ibs. 



In Warr's tAmstruotion of Machinery ,' a very useful oompantlv* 

 table of the various kinds of resistances of the principal classes of 

 materials used in the arts is given as follows : 



Tuble k from Warr's ' Construction of Machinery," of specific graving 

 i.l of the valut-K of N, the co-efficient of the s|><-cific strength of m.v 

 or the application oi tin- formula iiHually i-:nployed to calculate the 

 rotting weight of beam*, 1 ' 1 ' 1 " 1 H - 1 "!" 1 ' v * m bnjaki]] wc - Ut 



length in feet 

 u Ibs. ; both the breadth and depth bring in inches. 



500 



3'JO 



481 



200 



424 



4:12 



350 



JOS 



430 



527 



1980 



78 



69 



64 



TABLZ, iiv ME. BM-AX, or MODCI.I OF TORSIOX or WOODS. 



