Secondary radiation in cadmium vapor containing mercury as an impurity.---Attention is called to the points of difference between the conditions under which the two types of optically excited spectra of mercury vapor appear, namely resonance radiation and fluorescence. In the present experiments it is noted that when a bulb containing cadmium with a slight impurity of mercury is illuminated by light of 2288A wave-length the secondary radiation contains the mercury line 2536.7A in addition to the cadmium lines 2288A and 3261A provided the metal is distilling. As soon as the vapor is stagnant, however, only the cadmium 2288A line appears. The suggestion is made that the phenomenon is due to the presence in the distilling vapor of unstable HgCd molecules. In such a molecule the Cd atom may absorb the 2288A radiation and subsequently in the breakdown of the molecule may excite the Hg atom by a collision of the second kind.Polarization of the cadmium resonance, radiation in zero magnetic field.---The polarization of the cadmium resonance radiation (3261A) in zero magnetic field under certain conditions was found to be 35 percent. In order to explain this value by the kinetic theory, one must assign effective radii to the colliding atoms which are thirty times the radii effective in ordinary collisions.Secondary radiation in cadmium vapor containing mercury as an impurity.---Attention is called to the points of difference between the conditions under which the two types of optically excited spectra of mercury vapor appear, namely resonance radiation and fluorescence. In the present experiments it is noted that when a bulb containing cadmium with a slight impurity of mercury is illuminated by light of 2288A wave-length the secondary radiation contains the mercury line 2536.7A in addition to the cadmium lines 2288A and 3261A provided the metal is distilling. As soon as the vapor is stagnant, however, only the cadmium 2288A line appears. The suggestion is made that the phenomenon is due to the presence in the distilling vapor of unstable HgCd molecules. In such a molecule the Cd atom may absorb the 2288A radiation and subsequently in the breakdown of the molecule may excite the Hg atom by a collision of the second kind.Polarization of the cadmium resonance, radiation in zero magnetic field.---The polarization of the cadmium resonance radiation (3261A) in zero magnetic field under certain conditions was found to be 35 percent. In order to explain this value by the kinetic theory, one must assign effective radii to the colliding atoms which are thirty times the radii effective in ordinary collisions.

Physical ReviewMay 1, 19275 citations

Polarized Resonance Radiation in Weak Magnetic Fields

Robert Williams Wood, A. Ellett

Effect of a magnetic field on the polarization of resonance radiation of mercury and of sodium.---(1) Mercury $\ensuremath{\lambda}2536$. A beam of plane polarized monochromatic light was focussed on the bulb containing the vapor at low pressure (0\ifmmode^\circ\else\textdegree\fi{}C), and the polarization of the resonance radiation was determined photographically with the aid of a quartz wedge and a double image quartz prism. If the exciting beam is going east with the electric vector vertical, when the earth's field is carefully neutralized the polarization is 90 per cent in any horizontal direction and zero vertically; a field of only 2 gauss directed north reduces the polarization in its direction to nearly zero (the decrease with increasing field being exponential), changes the polarization east and also up to 60 percent, and increases the intensity directed upwards threefold. Similar effects are produced by fields in other directions. The polarization with zero field does not approach 100 per cent at low pressures, since 90 per cent was found also with the vapor at -50\ifmmode^\circ\else\textdegree\fi{}C, when the radiation first appeared. It was thought that the high value might be due to an orientation of the resonating atom by the field of the exciting light, but a beam of concentrated sunlight produced no effect. As found by Malinowski, a strong field of 10,000 gauss merely increased the intensity of the radiation about 10 per cent. This added light was found to be unpolarized. (2) Sodium $D$ line. In the case of sodium vapor the tube was heated to 185\ifmmode^\circ\else\textdegree\fi{}C, the observations were visual, and as a source of unreversed light, the glow on the surface of a sodium glass vacuum tube carrying a discharge, was used. The effects observed are similar to those for mercury, but differ for some directions; fields forty times stronger were required, and the polarization in zero field was only 6 per cent, probably due to traces of hydrogen. This was increased by the field in some directions to 30 per cent.Effect of magnetic field on fluorescent light of iodine vapor and on white scattered light from mercury and ether vapors.---The polarization was found not to be affected.Effect of a magnetic field on the polarization of resonance radiation of mercury and of sodium.---(1) Mercury $\ensuremath{\lambda}2536$. A beam of plane polarized monochromatic light was focussed on the bulb containing the vapor at low pressure (0\ifmmode^\circ\else\textdegree\fi{}C), and the polarization of the resonance radiation was determined photographically with the aid of a quartz wedge and a double image quartz prism. If the exciting beam is going east with the electric vector vertical, when the earth's field is carefully neutralized the polarization is 90 per cent in any horizontal direction and zero vertically; a field of only 2 gauss directed north reduces the polarization in its direction to nearly zero (the decrease with increasing field being exponential), changes the polarization east and also up to 60 percent, and increases the intensity directed upwards threefold. Similar effects are produced by fields in other directions. The polarization with zero field does not approach 100 per cent at low pressures, since 90 per cent was found also with the vapor at -50\ifmmode^\circ\else\textdegree\fi{}C, when the radiation first appeared. It was thought that the high value might be due to an orientation of the resonating atom by the field of the exciting light, but a beam of concentrated sunlight produced no effect. As found by Malinowski, a strong field of 10,000 gauss merely increased the intensity of the radiation about 10 per cent. This added light was found to be unpolarized. (2) Sodium $D$ line. In the case of sodium vapor the tube was heated to 185\ifmmode^\circ\else\textdegree\fi{}C, the observations were visual, and as a source of unreversed light, the glow on the surface of a sodium glass vacuum tube carrying a discharge, was used. The effects observed are similar to those for mercury, but differ for some directions; fields forty times stronger were required, and the polarization in zero field was only 6 per cent, probably due to traces of hydrogen. This was increased by the field in some directions to 30 per cent.Effect of magnetic field on fluorescent light of iodine vapor and on white scattered light from mercury and ether vapors.---The polarization was found not to be affected.

Physical ReviewSep 1, 192474 citations

D

line. In the case of sodium vapor the tube was heated to 185\ifmmode^\circ\else\textdegree\fi{}C, the observations were visual, and as a source of unreversed light, the glow on the surface of a sodium glass vacuum tube carrying a discharge, was used. The effects observed are similar to those for mercury, but differ for some directions; fields forty times stronger were required, and the polarization in zero field was only 6 per cent, probably due to traces of hydrogen. This was increased by the field in some directions to 30 per cent.Effect of magnetic field on fluorescent light of iodine vapor and on white scattered light from mercury and ether vapors.---The polarization was found not to be affected.