The absorption of X-rays

An account is given here of the measurement, by a balance method, of the mass-absorption coefficients of a number of elements, primarily relative to aluminium, over a range of wave-lengths from 0·3 to 0·7 Å. U., and of the absolute coefficient of aluminium itself for three wave-lengths. The main objection to the direct method of measuring absorption coefficients is the difficulty, with ordinary facilities, of obtaining an even approximately constant source of X-rays. This necessitates the use of some form of compensation or comparison method.