"'N 24 1921 
PROCEEDINGS ,/ 
OF THE 
NATIONAL ACADEMY OF SCIENCES 
Volume 2 AUGUST 15. 1916 Number 8 
THE ABSORPTION COEFFICIENTS OF SOFT X RAYS 
By C. D. Miller 
RYERSON PHYSICAL LABORATORY, UNIVERSITY OF CHICAGO 
Received by the Academy, June 14, 1916 
The X rays studied were produced at potentials ranging from '2500 
to 10,000 volts. The tube (see fig. 1) in which they were generated 
'was provided with a hot cathode, C, consisting of a flat spiral of tungsten 
wire, similar to the cathode in a Coolidge tube. The anode was of iron, 
but this has no bearing on the work reported here, as the characteristic 
radiation of iron did not appear in noticeable quantity. The rays 
escaped through an aluminum window, W, of 0.001823 grams per square 
centimeter, or of 0.000675 centimeters thickness, supported on wire 
gauze of 180 meshes to the inch. The rays, after passing through the 
sheets of absorbing material, entered the chamber of the gold leaf 
electroscope, by means of which their ionizing effect was measured. 
441 
