OF ARTS AND SCIENCES : FEBRUARY 14, 1865. 415 



bar of the same dimensions and material. Fairbalrn,* referring to his 

 experiments on the progressive deflection of bars of cast-iron, subjected 

 to a transverse strain for a period of about five years, remarks as 

 follows : — 



" Viewing the whole of these experiments in relation to the solution 

 of a problem affecting the laws which regulate the resistance of bodies 

 to continuous strain, it is important to observe how admirably the co- 

 hesive powers of matter adapt themselves to circumstances, and with 

 what tenacity they resist forces tending to dissever and rupture 'their 

 parts. 



" It is still a question for consideration how far this power extends, 

 and whether or not bodies, when loaded within even T^^g^r P^^*- ^^ their 

 breaking weight, would sustain the load forever, provided that no dis- 

 turbing cause were present to produce fracture. 



" I am strongly inclined to think that such would be the case, not- 

 withstanding the fact that the whole of the loaded bars exhibit a 

 progressive increase of deflection, which fact I am disposed to attribute 

 to the vibrations continually going on in the building where the bars 

 were fixed, and to those atmospheric changes, such as temperature, 

 oxidation, &c., to which every description of material is subject." 



I think we may safely infer that a pillar, not subject to disturbances, 

 may be loaded with a very large proportion of its breaking weight, say 

 ■j^^, or more, for a time indefinitely long without breaking ; but that a 

 pillar, loaded with a weight a very little less than just sufficient to 

 break it in a short time, will be liable to break within an indefinitely 

 long time ; and that this time will be much shortened if the pillar is 

 subject to vibration. 



Pillars in some situations, such as warehouses, are subject to concus- 

 sions from bodies falling on a floor above ; the effect of this on the pil- 

 lar would be much weakened by the mass of the floor, and it can 

 scarcely happen when the pillar is otherwise loaded to the full extent 

 it is designed to support. 



"We have seen that the formulas for the breaking weight are de- 

 duced from experiments made on small pillars, very carefully cast 

 from iron of superior quality ; when the same formulas are applied to 

 pillars made of iron of inferior quality for the purpose, and are less 

 carefully cast, it is reasonable to expect that the computed breaking 



* On the Application of Cast and Wrought L'on to Building Purposes. By 

 William Fairbairn. London, 1854. 



