PROCEEDINGS. 
425 
Mr. Wear read some items from the last Report of the Director 
of Harvard Observatory. 
Mr. R. A. Harris presented a paper on The feasibility of 
measuring tides and currents at sea. The use of piano-wire 
sounding-apparatus was suggested, and the errors were discussed 
that might arise from the weight of the wire, impulse of the cur¬ 
rent, or inaccurate estimate of vertically at the upper end of the 
wire. [Published in Science, vol. xix, p. 704 (1904).] 
The paper was discussed by Mr. Marvin. 
Mr. F. J. Bates then spoke on The effect of a magnetic field 
on plane-polarized light. Starting with Faraday’s experiment 
in 1849, the historical development of the subject was followed 
down to the speaker’s work on the rotary dispersion of sub¬ 
stances having anomalous dispersion, as solutions of fuchsine. 
No anomaly was found in the rotation, such as former observers 
had reported, although the speaker’s apparatus was ten times as 
sensitive as theirs; the reported effects were traced to constant 
errors, which were avoided by a new method of observing. [Pub¬ 
lished in Annalen der Physik, vol. xii, p. 1080 (1903).] 
The paper was discussed by Messrs. Buckingham, Bigelow, 
Guthe, and Bauer. 
581st Meeting. February 27, 1904. 
President Marvin in the chair. 
Sixty persons present. 
Mr. A. F. Zahm, in a paper on Atmospheric friction with spe¬ 
cial reference to aeronautics, presented some results from his 
three years’ experiments. He finds the skin-friction to vary 
nearly as the length of surface, and as the velocity to the power 
1.85, and within wide limits to be independent of the surface 
material, provided it is smooth. To overcome the friction on the 
surface necessary to support 100 pounds, under practical condi¬ 
tions of flight, would require about one horse-power on a tow-line, 
or nearly two horse-power applied by propellers. [Published in 
this volume, p. 247; Phil. Mag., July, 1904.] 
Mr. C. M. Manley then spoke on the History and present 
status of aeronautics. He traced briefly the development of 
