- 13 - 



the northwest corner and connected to the fluid system by a tun- 

 nel of suitable dimensions. The horizontal scale being thus 

 fixed, and considering the desirability of a time scale of one 

 mean solar minute per mean solar day, the vertical scale was cal- 

 culated from the kinematic formula of Froude for the distorted 

 open channel model in v«rhich the value of g and properties of water 

 are substantially the same for the model and the prototype. 



1 

 — (2) 



193 



This vertical scale is within half of one per cent of 1/16 inch 

 per "foot" and was so adopted. The resulting vertical distortion 

 is 



L 192 1 



D^ = j: = (3) 



y 20,000 104 



This amount of vertical distortion is acceptable. 



The Froude velocity scale is derived fjrom consideration of 

 the rate of progress of a gravity wave of very great length com- 

 pared with the depth of water; that is of tidal dimensions. The 

 rate of progress of such a wave is given by Vg d, where g is the 

 acceleration of gravity and d is the depth of water. The accelera- 

 tion of gravity is substantially the same in both the model and 

 prototype hence the velocity ratio is entirely controlled by the 



