SINCE Moseley's discovery of the fundamental laws of the X-ray emission, it has become quite clear that the most simple and conclusive characteristic of a Chemical element is given by its X-ray ...

IN a previous letter (NATURE, March 10, p. 322) we have shown that the optical spectrum of the new element hafnium, of atomic number 72, which was discovered a short time ago by Coster and Hevesy ...