PROCEEDINGS. 
379 
but its nature and relationships have been much discussed. The 
speaker now finds that it is a barnacle, and that former errors 
arose from depending on broken specimens. [Published in 
Science, vol. xv, p. 5 (1902).] 
Mr. J. F. Hayford answered the question, What is the center 
of an area or the center of a population ? pointing out especially 
the inexactness of the popular notion that the latter center is the 
point that has as many people on one side of it as on the other; 
in practice this would give as many centers as there were pairs 
of intersecting lines.’ This was illustrated by an ingenious 
model. The only definition that gives a single point is that 
corresponding to the center of gravity of an area. [Not pub¬ 
lished.] 
Mr. 0. H. Tittmann read from an article published by Prof. 
Hilgard in 1872 on movements of the center of population in the 
United States. 
The paper was discussed by Messrs. Ball, Thomson, Upde- 
graff, and We ad. 
542d Meeting. December 7, 1901. 
Vice-President Gore in the chair. 
Thirty persons present. 
Mr. Radelfinger presented a curious series that he has met 
with in differentiating a complex variable. 
Mr. T. J. J. See, of the Naval Observatory, presented his re¬ 
sults on the Diameters of the planets as measured in daylight. 
The measures were made near the close of the day, and the sky 
being partially lighted, the error from irradiation was reduced 
or removed entirely. This error for Venus was estimated as 
0".72. The result is to diminish the diameters observed at 
night by from 0".25 for Neptune to 0".75 for Jupiter. These 
diameters for Jupiter and Saturn appear to be reliable to 
1/1000. Measures on Jupiter’s satellites and Titan were also 
given. As a consequence of the reduced value of the diameters, 
the density of the planets will be increased. [Results incor- 
