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The decay of the fluorescence of uranyl salts has been measured at 293°, 77°, and 4°K with a photoelectric gate circuit technique. The resultant mean lives of the excited states in general increase sharply with decreasing temperatures. This indicates that at the higher temperatures where relaxation times as low as 50 microseconds are found the upper states are destroyed chiefly by interaction with the crystal lattice. The lifetime of the undisturbed UO_2 ion must be more than 2 milliseconds. This is in agreement with the brightness of the fluorescence which normally increases in proportion with the mean life.

The spectral of the rare earths have been photographed under controlled excitation so that either the spectra of the doubly or triply ionized elements are brought out with maximum intensity. A mild excitation is used in addition to give the first and second spectra for comparison. Some regularities are immediately apparent and vary very gradually through the rare-earth group. The general features of the spectra are discussed in this paper.

More then 2600 new lines have been measured in the emission spectra of H_2 and D_2 between 1.15 and 1.97 μ, with lead sulfide cells and powerful discharge tubes. Most of the strong lines below 1.65 μ belong to known band systems. Beyond this, new and so far incompletely analyzed band systems become prominent.

Interferometric wavelength measurements (3570 A to 5709 A) are given for 189 iron lines produced by a hollow cathode discharge. The lines are considerably sharper than those of the iron arc and the available evidence shows that the wavelengths are invariant with any changes in operating conditions of the tube. The hollow cathode discharge tube in neon with iron electrodes appears to be the best source of standards for wavelength measurements.

A sealed-off hollow cathode discharge tube with iron electrodes and rare gas filling is described which will give an iron spectrum with very sharp lines and intensities of high reproducibility. Extensive data are given of the dependence of the iron intensities on the character of the rare gas, its pressure, and the discharge current. For most purposes a neon filling at about 3 mm pressure is recommended. The lines of such a tube are recommended for wavelength standards. They may serve as intensity standards with the proper precautions.

The absorption and fluorescence spectra of DyCl_3·6H_2O have been observed at 4.2°K and 77°K. This makes an analysis of the low-lying levels possible including their Stark splitting. The strong lines have been interpreted as transitions between the ^6H, ^6P, and ^6F multiplets. The Zeeman effect gives a splitting of s^1 = 6.73 if the acute bisectrix is parallel to the field.

An arrangement is described by which spectroscopic wavelength measurements are greatly simplified with an increase in accuracy. The measuring microscope is replaced by a photoelectric scanning device which displays line contours on an oscilloscope screen. The comparator readings are made automatically with electronic devices, and the results either recorded with an automatic typewriter or punched into cards or both. Photographic densities are measured and recorded at the same time. The data are then further processed by electronic calculating machines.The equipment is built largely from commercially available components. Its operation is simple and foolproof. The various stages are independent of each other and can be introduced singly or in combination as desired.

Interferometric wavelength measurements (3570 A to 5709 A) are given for 189 iron lines produced by a hollow cathode discharge. The lines are considerably sharper than those of the iron arc and the available evidence shows that the wavelengths are invariant with any changes in operating conditions of the tube. The hollow cathode discharge tube in neon with iron electrodes appears to be the best source of standards for wavelength measurements.

A sealed-off hollow cathode discharge tube with iron electrodes and rare gas filling is described which will give an iron spectrum with very sharp lines and intensities of high reproducibility. Extensive data are given of the dependence of the iron intensities on the character of the rare gas, its pressure, and the discharge current. For most purposes a neon filling at about 3 mm pressure is recommended. The lines of such a tube are recommended for wavelength standards. They may serve as intensity standards with the proper precautions.

With the help of an automatic electronic switch placed between phototube and recorder of a spectrograph, the intensities as function of time of a series of spectrum lines produced in a spark have been recorded. The changes as function of the position in the gap were also investigated. There is an extensive afterglow which in general decays faster for the higher stages of ionization. The continuous background has the same characteristics as the spectrum of the surrounding gas. The changes in self-absorption excitation and line profile were also studied as function of time and partly correlated with the fundamental processes responsible for the afterglow.

Groups of iron lines with relative intensities independent of excitation are proposed to serve as intensity standards for rapid and reliable plate calibration. One such group between 3140 and 3240A has been tested under a great variety of conditions and found to be satisfactory for this purpose. Lines of Fe I selected at random in general have their relative intensities changed much more by self-reversal than by changes in excitation. A general quantitative study of self-reversal was made which allows an estimate of the degree of self-reversal of any line under given conditions. Weak or moderately strong lines coming down to all but the lowest levels are free from self-reversal under the conditions at which arcs or sparks are usually operated.

An electronic device is described which renders a phototube sensitive only at prescribed but arbitrary intervals of a spark cycle. Such undesirable light, as air lines and continuous background, can then be suppressed. There is evidence that for spectrochemical analysis purposes the spectrum thus recorded photoelectrically combines the stability and reproducibility of the condensed spark with the sensitivity of the dc arc.

Examination of the light output of discharge tubes, using the multiplier-type photo-tube in conjunction with a cathode-ray oscillograph, is suggested as a powerful aid to the usual electrical measurements in understanding the behavior of electrical discharges in gases. Exhaustive experiments of this type are under way, the preliminary results of which are reported in this paper. A striking characteristic of these results is the appearance of oscillations not only in the voltage and current, but particularly in the light intensity. These oscillations appear to be very general, and are not due to the external circuit used. They are only of a few percent magnitude in the case of the voltage and current, but often nearly 100 percent in the case of the light intensity. It seems certain that the theory of electrical discharges should in many cases be revised to take these oscillations into account.

A study of the Zeeman effect of absorption lines of GdCl_3·6H_2O and its dependence on the orientation of the crystal has given the constants for the magnetic ellipsoids for the ground state and 11 excited states. Evidence is presented for identifying the first three absorption groups as transitions from ^8S to ^6P_7/2, ^6P_5/2, and ^6I_7/2. The magnetic observations were made at 77°K, 4.2°K, and 1.7°K and field-free spectra also taken at 195°K and 273°K. Very strong fluorescence is observed from the lowest excited state to the ground state.The magnetic axes are approximately but not exactly the same for all observed states. The direction of maximum susceptibility is not that of the twofold crystal axis but perpendicular to it. There are small but definite deviations from isotropic magnetic behavior for the ground state.

The absorption and fluorescence spectra of DyCl_3·6H_2O have been observed at 4.2°K and 77°K. This makes an analysis of the low-lying levels possible including their Stark splitting. The strong lines have been interpreted as transitions between the ^6H, ^6P, and ^6F multiplets. The Zeeman effect gives a splitting of s_1=6.73 if the acute bisectrix is parallel to the field.

An arrangement is described by which spectroscopic wavelength measurements are greatly simplified with an increase in accuracy. The measuring microscope is replaced by a photoelectric scanning device which displays line contours on an oscilloscope screen. The comparator readings are made automatically with electronic devices, and the results either recorded with an automatic typewriter or punched into cards or both. Photographic densities are measured and recorded at the same time. The data are then further processed by electronic calculating machines.The equipment is built largely from commercially available components. Its operation is simple and foolproof. The various stages are independent of each other and can be introduced singly or in combination as desired.

The absorption spectrum of YbCl_3·6H_2O has two sharp lines near 9700 A which are interpreted as the transitions from the M=5/2 Stark component of the ^2F_7/2 level of the Yb^+++ ion to the M=3/2 and 5/2 levels of the other doublet component ^2F_5/2. The Zeeman splittings of the two lines were investigated at 4°K as a function of the orientation of the crystal. They can be interpreted by assuming that the crystal field has a pronounced magnetic symmetry axis (probably sixfold) perpendicular to the twofold symmetry axis of the crystal. The magnetic ellipsoid is degenerate into a pair of planes perpendicular to this axis. The direction of the magnetic axis is slightly different for the three observed states and bears no relation to the optic axes of the crystal.

The spectral of the rare earths have been photographed under controlled excitation so that either the spectra of the doubly or triply ionized elements are brought out with maximum intensity. A mild excitation is used in addition to give the first and second spectra for comparison. Some regularities are immediately apparent and vary very gradually through the rare-earth group. The general features of the spectra are discussed in this paper.

The decay of the fluorescence of uranyl salts has been measured at 293°, 77°, and 4°K with a photoelectric gate circuit technique. The resultant mean lives of the excited states in general increase sharply with decreasing temperatures. This indicates that at the higher temperatures where relaxation times as low as 50 microseconds are found the upper states are destroyed chiefly by interaction with the crystal lattice. The lifetime of the undisturbed UO_2 ion must be more than 2 milliseconds. This is in agreement with the brightness of the fluorescence which normally increases in proportion with the mean life.

The relative intensities of 478 nickel arc lines have been measured photoelectrically between 3359 and 5893A with an accuracy of better than one percent for the good lines. The dc arc was operated under steady conditions at a current of 2 amperes. Corrections for self-absorption have been determined. The influence of arc fluctuations has been minimized by recording always the ratio of the output of a scanning tube to that of a fixed tube placed on a control line.

Details are given for an electrodeless hydrogen discharge tube excited in a microwave cavity. The tube is extremely simple in construction. The hydrogen is stored as UH_3. The excitation is efficient, and the spectrum is obtained with great strength and purity. Discharge conditions can be held constant much better than in the conventional tubes.

Details are given for an electrodeless hydrogen discharge tube excited in a microwave cavity. The tube is extremely simple in construction. The hydrogen is stored as UH_3. The excitation is efficient, and the spectrum is obtained with great strength and purity. Discharge conditions can be held constant much better than in the conventional tubes.

The absorption spectrum of YbCl_3·6H_2O has two sharp lines near 9700 A which are interpreted as the transitions from the M = 5/2 Stark component of the ^2F_7/2 level of the Yb^+++ ion to the M=3/2 and 5/2 levels of the other doublet component ^2F_5/2. The Zeeman splittings of the two lines were investigated at 4°K as a function of the orientation of the crystal. They can be interpreted by assuming that the crystal field has a pronounced magnetic symmetry axis (probably sixfold) perpendicular to the twofold symmetry axis of the crystal. The magnetic ellipsoid is degenerate into a pair of planes perpendicular to this axis. The direction of the magnetic axis is slightly different for the three observed states and bears no relation to the optic axes of the crystal.

More then 2600 new lines have been measured in the emission spectra of H_2 and D_2 between 1.15 and 1.97 µ, with lead sulfide cells and powerful discharge tubes. Most of the strong lines below 1.65 µ belong to known band systems. Beyond this, new and so far incompletely analyzed band systems become prominent.