41« 



THE STRENGTH 



ally take place ; and, hence, there is some 

 intermediate point or line, between the top and 

 bottom of the beam, where the particles are 

 neither extended nor compressed: all above 

 being in some state of tension, and all below 

 compressed. This line may properly be called 

 the neutral hne. 



If then, ADBC represent a transverse surface 

 of the beam, and AB the neutral line, ADB 

 must be the surface of tension, and ACB that 

 of compression. 



Now, it is evident, that the extensions or 

 compressions of any particles within these sur- 

 faces, will be as their distances from the line 

 AB ; and the forces, exerted by those particles, 

 must be in the same proportion, so long as the 

 elasticity remains perfect ; for then the forces are 

 found to be as the extensions or compressions. 

 Afterwards, the forces of the particles would 

 be as some different functions of their distances 

 from the neutral line. 



