434 
PHILOSOPHICAL SOCIETY OF WASHINGTON. 
and the determinations agreed to 1/5 per cent. Interfering 
trains could be compared, one of which was damped and the other 
controlled by polarizing mirrors. [Not published.] 
The paper was discussed by Messrs. Rosa, Marvin, and Buck¬ 
ingham. 
592d Meeting. December 10, 1904. 
Mr. L. A. Bauer in the chair. 
Eighteen persons present. 
Mr. H. H. Kimball read by invitation a paper on Variations 
in insolution and in the polarization of blue skylight in 1903-04. 
It appears that the quantity of solar radiation reaching the earth 
on clear days in 1903 was 16 per cent, less than in 1902, and 
9 per cent, less than in 1904. The percentage of polarization at 
the maximum point in the summer of 1904 was 49.6 as compared 
with 40.6 in 1903. [Published in Proc. Third Convention of 
Weather Bureau Officials at Peoria, 1904; Monthly Weather 
Review, vol. xxxiii, p. 100 (1905).] 
The paper was discussed by Messrs. Bauer, Fowle, Hayford, 
and Wead. 
Mr. J. F. Hayford then discussed The computation of deflec¬ 
tions of the vertical from the surrounding topography. By an 
ingenious method, partly graphical, it had been found practical 
to compute for each of some 200 stations the deflection due to the 
attraction of all the elevated land-masses within a radius of 2500 
miles. When these computed deflections from known causes are 
combined with the deflections found from geodetic measure¬ 
ments, the quantities to be explained by irregularities within the 
earth’s surface come out many times larger than had been sup¬ 
posed heretofore. [Not published.] 
593d Meeting. December 24, 1904. 
THIRTY-FOURTH ANNUAL MEETING] 
Vice-President Day in the chair. 
Six members present. 
