388 PHILOSOPHICAL SOCIETY OE WASHINGTON. 
Mr. M. Updegraff prJtented a paper on The stability of astro¬ 
nomical piers. The earliest astronomical instrument was merely 
a pier, the gnomon, and by it the ancients determined a large 
number of constants. The experience at various observatories 
with stone, iron, and brick piers was described, and the defects 
which have led to the replacing of the marble piers of the 6-inch 
circle at the Naval Observatory by brick rising from a great con¬ 
crete base, were explained. [Not published.] 
In the discussion Mr. Paul described his experience with a 
telescope mounted on a pier built directly on a rock exposed to 
the sun’s action, and Mr. Green spoke of the long time needed 
for concrete to reach a permanent condition. Eemarks were 
also made by Messrs. Bauer and Wead. 
546th Meeting. January 18, 1902. 
Vice-President Gore in the chair. 
Thirty-six persons present. 
Mr. L. P. Shidy read a paper on An explanation of the cur¬ 
rents in Unalga Pass, Aleutian Islands, Alaska. These high 
currents are due to a difference in level at the ends of the Pass, 
owing to the fact that high water occurs at different times; their 
velocity seems to be closely proportional to the square root of the 
difference of level, following Torricelli’s law. [Not published.] 
Mr. Ball spoke of the violence of these currents, and of the 
unaccountable dying away of the wind at the middle of the Pass. 
Mr. J. H. Gore then gave an account of the proposed drain¬ 
ing of Zuyder Zee, illustrating the paper by many lantern slides. 
The plan recommended by the large commission appointed in 
1892 calls for the reclamation only of those portions that have a 
clay bottom; so the mouths of the rivers and the present routes 
of water communication would be undisturbed. A great sea 
dike would be required at the north end, with many locks and 
sluiceways to be opened at the hours of low tide. This would re¬ 
quire ten years and cost $16,000,000. Then an area of 52,000 
acres in the northwest part would be diked and pumped out, at a 
cost of $5,000,000. Finally, about a million and a quarter acres 
