PHYSICS: A, G. WEBSTER 263 
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FIG. 4 
The emergence of the bullet from the barrel is shown by the interruption 
of a beam of light thrown upon the film by a separate mirror. 
In a subsequent paper the theory of the apparatus and the conclusions 
that may be obtained from it, including the resistance in the barrel and the 
variation of specific heats will be described. 
ON THE ANGLE OF REPOSE OF WET SAND 
By a. G. Webster 
Ballistic Institute, Clark University, Worcester, Massachusetts* 
Read before the Academy, April 29, 1919 
It is well known that sand, gravel, broken stones, grain, sugar or any pul- 
verulent substance has a definite angle of limiting steepness which is called 
the angle of repose. In Dr. Breasted's lecture the pile of debris in front of 
the Temple of Thebes showed such a definite angle. In driving to Washing- 
ton last week I passed along the Cape Cod Canal and noticed a very definite 
angle of repose for the sand alongside the Canal. Passing by the beach at 
Narragansett Pier I measured its slope and found it to be very uniform and 
about one in fourteen. 
* Contribution from the Ballistic Institute, Clark University, No. 6. 
