The diffraction of x-rays.

Abstract

It is a great honour to be invited to give a lecture which bears the name of that many-sided and interesting man, Silvanus Thompson, who was a pioneer in such very varied fields, and I thank you warmly for the invitation which has brought me here tonight. Silvanus Thompson had many links with the Royal Institution where I now work, and frequently lectured there. And if I wanted another association with the Royal Institution, I noticed as I came along Welbeck Street to this hall a plaque on a house commemorating the fact that Thomas Young had lived there. Thomas Young was one of the first professors in the Royal Institution at the beginning of the nineteenth century and with Humphry Davy he laid the foundations of its fame. Young established the wave theory of light by his experiments on interference. Silvanus Thompson was, I suppose, the first in this country to repeat Röntgen's experiments with X rays, and as I am to talk tonight on the interference of X rays, the omens ought to be favourable. The diffraction of X rays, and the analysis of crystals by its aid, is an extraordinary subject. The physical principles are extremely simple. X rays fall on the atoms of the regular crystalline pattern and are scattered by them. These scattered waves interfere with each other, so that in some directions a strong diffracted beam is produced and in others it is weak.