Crookes, Proc. Roy. Soc. 81, p. 405, 1903.

Elster and Geitel, Phys. Zeit. No. 15, p. 437, 1903.

Glew, Arch. Röntgen Ray, June 1904.

Becquerel, C. R. 137, Oct. 27, 1903.

Tommasina, C. R. 137, Nov. 9, 1903.

An interesting side-light is thrown on this question by the experiments described in Appendix A of this book.

Rutherford and Miss Brooks, Phil. Mag. July 1902.

In order to obtain a thin layer, the compound to be tested is ground to a fine powder and then sifted through a fine gauge uniformly over the area, so that the plate is only partially covered.

Rutherford, Phil. Mag. Jan. 1899.

Owens, Phil. Mag. Oct. 1899.

Rutherford and Miss Brooks, Phil. Mag. July, 1900.

Since the ionization at any point above the plate is the resultant effect of the α particles coming from all points of the large radio-active layer, λ is not the same as the coefficient of absorption of the rays from a point source. It will however be proportional to it. For this reason λ is called the “absorption constant.”

Townsend, Phil. Mag. Feb. 1901.

Durack, Phil. Mag. July 1902, May 1903.

Bragg and Bragg and Kleeman, Phil. Mag. Dec. 1904.