444 THE STRENGTH 



this last tendency is resisted by all the particles 

 in the section. Thus, in the figure to article 4, 

 the force of compression is not in the direction 

 Gf produced, but in a direction downwards, 

 oblique to that. It is composed of the force 

 in Gf produced, and that part of the weight 

 W, whose vertical effect is sustained by the 

 lower part of the beam. This compounded 

 fol'ce will then tend to separate the compressed 

 part of the beam in the form of a wedge, and 

 this tendency must be resisted by the strength 

 of the part between the ribs, or flanges. We 

 have already given one instance of fracture this 

 way, and there will occur several others in the 

 course of our experiments. 



34. We see then that there are three probable 

 ways in which a beam might break, 1st, by 

 tension, or tearing asunder the extended part; 

 2nd. by the separation of a wedge, as above; 

 and 3rd, by compression, or the crushing of 

 the compressed part. I have not however 

 obtained a fracture by this last mode in cast 

 iron. 



35. Before giving a detail of the experiments 

 relative to this subject, made through the 

 medium of Messrs. Fairbairn and Lillie, I will 

 first describe an attempt which I had previously 



