The electron, its isolation and measurement and the determination of some of its properties

by Robert Andrews Millikan

series, which have uniformly from seven to eight times the wave-length of the

series. The plate opposite [p. 200] shows some very beautiful photographs taken by De Broglie in Paris[147] in October, 1916.

The upper one is the X-ray emission spectrum of tungsten. It consists of general radiations, corresponding to white light, scattered throughout the whole length of the spectrum as a background and superposed upon these two groups of lines.

Fig. 21a—PHOTOGRAPHS OF THE SPECTRA OF THE CHARACTERISTIC X-RAYS FROM CERTAIN SUBSTANCES

The remarkable element in these photographs is the exact similarity of the spectra produced by the different elements and the step-by-step shortening of the wave-length (which is proportional to the distance from the line on the left to the spectral lines) as the atomic number

increases. This is shown both in the