. The Bell System technical journal . preciably weakened, and did not at-tain their maximum intensities until the pattern of the third type hadalmost disappeared. The curve marked Type-4 in Fig. 5 shows thelife history of a typical beam of this type following a heat treatment ofthe crystal. In this particular experiment intensity measurementswere not made after sixty-one minutes. The dashed continuation ofthe curve represents its general course as known from other experi-ments. The two curves of Fig. 5 represent a single experiment which wascarried out at a time when the vacuum condition of ou
. The Bell System technical journal . preciably weakened, and did not at-tain their maximum intensities until the pattern of the third type hadalmost disappeared. The curve marked Type-4 in Fig. 5 shows thelife history of a typical beam of this type following a heat treatment ofthe crystal. In this particular experiment intensity measurementswere not made after sixty-one minutes. The dashed continuation ofthe curve represents its general course as known from other experi-ments. The two curves of Fig. 5 represent a single experiment which wascarried out at a time when the vacuum condition of our experimentalapparatus was intermediate between the best and the worst conditions39 598 BELL SYSTEM TECHNICAL JOURNAL which we were able to reahze. Under our best vacuum conditions,the intensity changes took place more than twenty times more slowlythan the changes shown in Fig. 5, and under our poorest vacuum con-ditions they took place so rapidly that the diffraction patterns of thethird and fourth types could not be found. AZIMUTH. Fig. 6—Scattering curves in a (110) azimuth of the crystal showing the tran-sient electron diffraction beams of the fourth type. On each arrow indicating theprimary beam is printed the wave-length of the electrons giving rise to the curve. The entire diffraction pattern of the fourth type is exhibited by thecurves of Figs. 6-8.^ These figures show a series of electron scatteringcurves in each of the principal azimuths of the crystal. When these (lit} AZIMUTH
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