398 
PHILOSOPHICAL SOCIETY OF WASHINGTON. 
The communication was discussed by Messrs. Paul, Hazard, 
and Abbe. 
Mr. G. K. Gilbert read a paper on The mechanism of vol¬ 
canoes. The speaker accepted Dutton’s views, but illustrated 
them from his own observations. The first problem is why the 
lava rises; the primary force is gravitation, and the column of 
lava must exert less pressure in the depths than the neighboring 
solid rocks; so to become light enough to rise, the heavy basic 
lavas, as basalt, must be heated till they are very fluid, while the 
lighter acid lavas will rise in a very viscous condition and flow 
slowly. The flow ceases because the matter which is lighter than 
the crust is exhausted. It is not yet clear how the liquid makes 
its way through the crust. An eruption may be dry, or wet, or 
explosive. [Published under the title “The Mechanism of the 
Mont Pelee Spine,” in Science, N. S., vol. xix, No. 294, June 17, 
1904, pp. 927-928.] 
The paper was discussed by Messrs. Bauer, Abbe, Paul, and 
McGee. 
Mr. A. F. Zahm then presented a paper on New methods of 
experimentation in aerodynamics, outlining some of the re¬ 
searches carried out by him and Mr. H. Mattullath in the 
laboratory of aerodynamics erected bv the latter at the Catholic 
University, and describing the instruments. A practically uni¬ 
form wind is produced in a tunnel 50 feet long by 6 feet square; 
in this various objects are held to determine the drift, lift, skin 
friction, etc. Pressures are read to one-millionth of an atmos¬ 
phere. [Published in part in the Physical Review, Dec., 1903.] 
555th Meeting. October 11, 1902. 
President Rathbun in the chair. 
Fifteen persons only were present, the night being stormy. 
Mr. Hayford gave a brief account of recent gravity observa¬ 
tions at the North Tamarack mine, Michigan, in which he had 
assisted, and spoke of the anomalous plumbline divergence, and 
the failure of steel balls dropped down the 4,600-foot shaft to 
reach the bottom. 
