. Carnegie Institution of Washington publication. 234 FLUORESCENCE OF THE URANYL SALTS. Laborde,1 which included a rotating pattern to hide the specimen from the observer during excitation by the spark from an induction coil, and later uncover the specimen. Wm. Crookes,2 in his study of the cathode phosphorescence of yttria, noted that the color at the beginning of decay was different from that observed after the decay had continued for a short period, and accordingly devised a phos- phoroscope to study this change. Figure 4 serves to show that it was of the sectored-disk form and driven by co
. Carnegie Institution of Washington publication. 234 FLUORESCENCE OF THE URANYL SALTS. Laborde,1 which included a rotating pattern to hide the specimen from the observer during excitation by the spark from an induction coil, and later uncover the specimen. Wm. Crookes,2 in his study of the cathode phosphorescence of yttria, noted that the color at the beginning of decay was different from that observed after the decay had continued for a short period, and accordingly devised a phos- phoroscope to study this change. Figure 4 serves to show that it was of the sectored-disk form and driven by cord and pulley. At a convenient distance was located an induction coil whose primary circuit was alternately made and broken by a commutator near the end of the revolving shaft C. The brushes could be so shifted as to cause the excitation of the phosphorescent substance P when an opaque sector passed between P and the eye. It was possible to change the period of decay by changing the speed or by changing the phase of the brushes relative to the edge of the sector. The phosphorescent substance was mounted in a convenient form of cathode-ray tube and excited by the dis- charge from the secondary of the coil. With the aid of the spectrometer, Crookes discovered that different lines appeared in the spectrum of the phosphorescent yttrium after second than at FIG. 4. Ph. Lenard3 devised a phosphoroscope which differs from the preceding forms, since no revolving disk is employed. To hide the specimen from view during excitation he used the motion of a screen mounted on the plunger of a Ruhmkorff mercury interrupter. The frequency of the interrupter was de- termined by that of the spring fork on which it was balanced; hence change in the period between excitation and observation was accomplished by chang- ing forks. The discharge of a condenser in parallel with secondary circuit of the coil was thus timed by the interruptions of the primary circuit to occur whil
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