A. B. Wood 185 
Effect of reducing depth of woter (in /, mm. steps 
Water Initially 2-0 deep. Wavelength 2°65 mr 
Bottom rubber 4 plate glas 
Fig. 10.25. Picture showing the effect of small changes in depth of water. The 
top picture is for 50 mm depth, and successive pictures from top to bottom made 
at decrements of 0.5mm. The bottom is plate glass and the frequency is 560 kcps. 
depths being 2.0, 1.0, and 0.75 in., respectively, when the bottom was rubber 
covering plate glass on steel. The frequency in this case was 560 kcps and the 
wavelength 2.65 mm, approximately. Compared with the pattern over a plate 
glass or steel bottom the 2-in.-depth record over rubber is comparatively sim- 
ple, but it is nevertheless much more complicated than the records in shallower 
water, the ratio of depth-to-wavelength in the three cases being roughly 20, 15, 
and 10. The relatively simple "corrugated" structure of the records in the last 
two cases is striking and is at present the subject of a mathematical analysis. 
In another series of records also at 560 kcps the bottom is plate glass 
overlying the steel of the tank, the depth of water being 2 and 1 in. The charac- 
