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PHYSICS: A. G. WEBSTER 
A few years ago a committee of this Academy was sent to Panama to ex- 
amine into the cause of the Culebra shdes. My interest was excited at that 
time, and a year ago by my being consulted as an expert on the collapse of a 
house. 
A few days ago it occurred to me, having a load of sand on the floor of my 
ballistic laboratory, to wet it and make an artificial beach. I found that on 
scraping it up with a board a very definite slope was obtained depending upon 
the wetness. I therefore requested my assistant Dr. E. A. Harrington to 
make a few quantitative experiments to determine the angle in terms of the 
wetness. This is shown in the figure. 
10 
Beginning with absolutely dry sand which was weighed in a tray a certain 
amount of water was added and the whole weighed. At first the added water 
is quickly absorbed and on account of the work done by the surface tension 
and the cohesion of the water a certain positive amount of cohesion is ob- 
tained by the sand, and it will remain in equilibrium vertically and even 
overhang. Of course these experiments are not extremely accurate. When 
a certain degree of wetness is passed the sand then acts like a plastic sub- 
stance, the degree of plasticity depending upon the relative amounts of water 
and sand. 
