310 WAVES OF THE SEA 



progress by gravitational transmission of pressure 

 in the manner postulated in the theory of long 

 waves. The conditions are so different from those 

 usually contemplated for long waves that such a 

 test is far from superfluous. 



True Velocity of Roll- Waves in the Griinnbach Conduit. 



There was, however, one observation which did 

 not agree with the theoretical numbers, and was 

 also out of accord with the other three observa- 

 tions, viz. : 



Calcu- 



Observed Observed Observed lated 

 Date. Depth Depth Speed Speed 



at Crest, at Trough. (F.P.S.). (F.P.S.). 

 Sept. 16, 1904 ... 8 in. 1*5 in. 3 4-60 



Or, putting it the other way, the calculated depth 

 at crest for the observed speed is only 4.6 inches, 

 the difference from the observed depth of 8 inches 

 being too great for error of observation. This 

 was the occasion of greatest observed wave de- 

 velopment on the Griinnbach, the depth of 

 i . 5 inches at trough being certainly small for the 



