5 2 Mayow 



driven into the mid-liquid, as it were with a hostile 

 blockade. 



OF THE RATIONAL CAUSE OF ELASTICITY 



So much then for the cause of rigidity. It remains 

 to inquire why rigid bodies when bent spring back of 

 themselves to their original shape — for in this lies the 

 explanation of elasticity. But to pave the way to 

 our view of the subject the following must be premised. 



In the first place, let us consider in how many ways 

 rigid bodies can be bent, and what sort of change as 

 to their shape they undergo when bent. Suppose then 

 a rigid body with its sides equal and parallel such as 

 that delineated in Plate I., Fig. 4. 



In the first place, this rigid body can be bent by 

 elongating its convex surface while the concave surface 

 remains of the same length as before inflexion, as is 

 shown in Plate I., Fig. 5, where let a^ c, 3, w, d^ be the 

 bent rigid body whose concave surface a^ c, is supposed 

 to be equal to the length of the rigid body before in- 

 flexion but whose convex surface b^ ;/, d^ is elongated 

 by as much as the line 3, ;/, d^ is longer than the line 

 a^ c. 



The second mode of bending a rigid body is that in 

 which the convex surface is drawn inwards towards 

 the concave surface — all the surfaces of the rigid body 

 retaining meanwhile their original length as is shown 

 in Plate I., Fig. 5, where let a^ c^ -b^ e^ d^ be the bent 

 rigid body whose convex surface 3, e^ d^ we suppose, 

 while the rigid body is bent, to be brought just so far 

 inwards as to be equal to the concave surface a^ c, 

 that is to the length of the rigid body before inflexion. 

 And indeed if all the sides of rigid bodies are to retain 

 when bent their original length, they can be bent in 



