arrivals. For all basement velocities that are obtained 
in deep sea refraction work, i.e e., Cn /ty greater than 
4.0, this factor may be taken equal to unity. 
Ve. Topographic Correction 
Areas of moderate to small topography were chosen 
for most of the deep sea refraction profiles; but before 
any calculations of basement velocity or depth can be made, 
it is necessary to remove the small effects of the irregu- 
larities in the bottom topography on the refraction travel 
timese A mean depth of water is chosen, and corrections are 
made plus and minus about this depth for the travel times of 
refraction arrivals. Difficulty arises in choosing what 
material the bottom topography takes place, whether it 
represents directly topography in the sediments or is a 
representation of the basement topography. The choice that 
is made depends on the type of t¥pography and structure 
involved. 
Figure 19 is a set of graphs of the corrections 
to be applied to the ground arrivals versus the difference 
in elevation of the bottom topography from the mean for 
various velocity contrasts between the material forming the 
bottom topography and the ocean. 
VI.- ‘Curved Ray Paths 
The time intercept for a refraction line in the 
simplest case of a single refracting layer is given by the 
(1) 
approximate formula, 
24 
eS 
C, Cy 
