The London, Edinburgh and Dublin philosophical magazine and journal of science . ction. This obliquely emittedradiation has to pass through a greater thickness of air before it hasreached the distance x from the infinite radioactive plane. Thus the re-lation between intensity and distance becomes greatly complicated. Itis impossible to calculate it without knowing the relation between theintensity of radiation from an element of .area, and the angle between thatelement and the direction of propagation. t Communicated by Prof. L. R. Wilberforce. X Annul. Phi/s. Chem. lxiv. 1, pp. 18-37 (1898).
The London, Edinburgh and Dublin philosophical magazine and journal of science . ction. This obliquely emittedradiation has to pass through a greater thickness of air before it hasreached the distance x from the infinite radioactive plane. Thus the re-lation between intensity and distance becomes greatly complicated. Itis impossible to calculate it without knowing the relation between theintensity of radiation from an element of .area, and the angle between thatelement and the direction of propagation. t Communicated by Prof. L. R. Wilberforce. X Annul. Phi/s. Chem. lxiv. 1, pp. 18-37 (1898). § Comptes Rendus, exxvi. pp. 5*21-523 (1898). 6S6 Mr. C. Gr. Barkla on Secondary after passing through another rectangular aperture in a leadscreen placed several centimetres from the side of the boxand parallel to it, the X-rays were not intercepted by any-solid body for a considerable distance—about two metres —but passed merely through air. To detect the secondary radiation, a special form of electro-scope was used. It consisted of a case (as shown in fig. 1), Fig. with four sides of stout brass. One end G wTas of glass, andat the opposite end a face of any desired material and thick-ness could be placed. As in C. T. E. Wilsons* experimentson Spontaneous Ionization, the gold-leaf and brass plate towhich it was attached were suspended in this case by a beadof sulphur S, which was fixed to the lower end of a verticalbrass rod R. This passed axially through a cylindrical brassneck N, whose lower end was movable along grooves in a* Boy. Soc. Proc. vol. lxviii. pp. 151-161 (1901). Radiation from Gases subject to X-Rays. 687 direction perpendicular to the two ends, and from which itwas separated by an ebonite plug P. Connexion could bemade between this rod and the insulated plate and gold-leafby means of a light spring K which was attached to the rod,and which when set in vibration made contact with theinsulated portion of the electroscope. The capacity of thiswas exceedi
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