Page:Popular Science Monthly Volume 83.djvu/249

Rh vibrations have only a very small amplitude. Koenigsbcrger and Küpfur and others consider that the band spectra of iodine, bromine, nitrogen peroxide, sulphur, iodine trichloride, nitrogen, etc., are due to a dissociation or recombination of the respective molecules, atoms or ions. In the case of iodine this change might be represented by the equation

At about 800° C. this reaction is about complete and the fme-banded absorption spectra should therefore disappear. Galitzin, Wilip, Evans and others have shown that the bromine absorption spectrum disappears as dissociation becomes more and more complete.

Canal rays have their source in positive ions that start in front of the cathode, move towards the cathode and pass through any openings in it with a velocity of about $$(10)^{8}$$ cms. per sec. After passing the cathode the canal ray particles may lose their charge or even become negatively charged. The spectrum lines of hydrogen, nitrogen, mercury, sodium, potassium, etc., emitted by canal rays show the Döppler effect when they are viewed in the direction in which the canal ray particles are moving. Accompanying the shifted lines are lines showing no displacement, "rest" lines due to centers that are comparatively at rest. The "rest" line is usually narrow while the shifted line, due to rapidly moving centers, is rather wide, the violet side of the line often being the sharpest. The width of the line indicates the range of velocity of the canal-ray emitting centers. Making certain assumptions as to the potential gradient through which the centers have passed. Stark has calculated the charge carried by centers emitting the various lines.

Since the "rest" and "shifted" lines are separated by a dark region. Stark concluded that canal-ray centers can only radiate line spectra when their velocity exceeds a certain critical value, this critical velocity increasing as the wave-length decreases. Increasing the purity of the gas increases the relative intensity of the "shifted" lines. Strosser has caused a stream of canal-ray centers to impinge into a current of a foreign gas. The "lines of the foreign gas were found to increase in intensity on leaving the cathode, pass through a maximum and then decrease in intensity. The intensity of the lines of the canalray centers decreased in intensity as the distance from the cathode increased.

Spark spectra have been photographed on rapidly-moving films by Schuster, Hemsalech, Schenck and others. The length of time the metallic vapor continued to emit line spectra was found to vary from