340 RECORDS. 



SECTION OF ASTRONOMY, PHYSICS AND 

 CHEMISTRY. 



May 2, 1904.'^ 



Section met at 8.25 P. M., Vice-President Poor presiding. 

 The minutes of the last meeting of Section were read and ap- 

 proved. 



The following program was then offered : 



R. S. Woodward, The Theory of a Double Suspension 

 Pendulum. 



C. 0. Trowbridge, Measurements of the Primary Feath- 

 ers OF recently killed Hawks, and their Bearings upon 

 THE Problem of Bird Flight. 



George B. Pegram, The Generation of Electrical 

 Charges by Radium. 



P. H. Dudley, Bending Moments in Rails, for the same 

 Superstructure, under Different Types of Locomotiyes. 



Summary of Papers. 



Professor Woodward described a double suspension pendulum 

 apparatus for determining the acceleration of gravity and gave a 

 brief outline of the theory of the apparatus. The latter consists 

 of two rectangular bars of brass, about twenty kilograms mass 

 each, connected by two steel tapes of equal length in such a 

 way that when one bar is held rigidly horizontal, the other bar 

 will be suspended horizontally by the equal and parallel tapes. 

 It was shown that when the suspended bar vibrates longitudi- 

 nally through small amplitudes its motion is very nearly the same 

 as that of a simple pendulum whose length is equal to that of 

 the tapes. It was shown also how small corrections due to the 

 mass of the tapes and to their rigidity may be applied in order 

 to get from the actual apparatus results in conformity with those 

 of a simple pendulum. 



Dr. Trowbridge stated that during the spring he had suc- 

 ceeded in obtaining a series of measurements of the primary 

 feathers of the hawk's wings, immediately after the death of the 

 birds, and secured additional proof of his theory that certain 



