4 Petavel, High- Pressure Explosions. 



The stiffness of a spring will vary with the material of 

 which it is made and its shape, increasing for a given size 

 as the shape approaches more nearly to that of a solid bar 

 subjected to longitudinal strain. This bar can be made as 

 short as may be desired, and, in theory, the time period of 

 the system is only limited b\' the density of the material 

 and by its modulus of elasticity. 



In practice, however, the travel of the moving parts 

 cannot be indefinitely decreased, for the deflections must 

 remain of such dimensions as to be accurately measurable. 



The following figure represents a recorder designed 

 on the principles we have just established. 



Fig. I. 



Diagiammalic Representation of llic Recording Manometer. 



A cylindrical groove is cut half through the walls of 

 the enclosure. The upper part P of the cylinder Jthus 

 obtained represents the piston of our indicator, and the 

 lower portion 5 the spring. Under the pressure of the 



