R. C. MILLER AND P. KUSCH TABLE II. Experimental conditions and results for measured velocity distribution distributions were shifted slightly to the high velocity side of the theoretical curves. The shift corresponds to re of the order of three percent higher the knife-edge copper slits was estimated to be 0 to 0.012 cm K 4662 628士2630土3 The potassium distributions were not extended 644-42 682*3 extension requires what appeared, at the time, to be a 9445 392=1 395+2 dangerously high speed of revolution. In the case of thallium, more complete distributions were obtained present work is to be a critical test of the Maxwellian The thallium distributions are quite similar to the distribution. The vapor pressures given in Table II potassium distributions already discussed. Runs 99 were obtained from the literature and represent the between experimental points and the theoretical curves question screpa ancies occur on the high-velocity side of the Of the three potassium distributions, Run 57 shown maximum, where there is a small excess of atoms in the in Fig. 4 provides the best agreement with the theo- retical curve. In this case, the vapor pressure in the experimental distribution. It should be noted that the oven was as low as wasexperimentally feasible. It was not experimental points could be plotted with the high possible to obtain velocity distributions for markedly tensities at the maximum velocity would no longer lower oven pressures since the beam intensity which coincide and the experimental distribution would then depends directly on the oven pressure, would then be appear to be deficient of atoms on the low-velocity so low that the several sources of noise would give data side. The observed discrepancies are again more of limited value long before statistical fluctuations pronounced at higher oven pressures ay a significant role. The experimental points are When thallium beams were observed, the tungsten seen to be in excellent agreement with the theoretical detector wire was constantly sprayed with oxygen to curve over the major part of the distribution. However, maintain a good oxidized surface on the wire. The velocity side of the maximum. The value of vr calculated from the oven temperature agrees with kept so small that the increase in pressure due to the experimental value It has been observed that the deficiency of atoms q ygen was about 5X10-8mm of mercury in the tector chamber and less in the other chamber on the low velocity side increases with increasing oven 2( pressures and with increasing slit depth. The deficiency 如如小m ▲RUN97 vapor pressure was markedly increased. The experi mental points of Run 60 are in good agreement with the theoretical curve in the neighborhood of the intensity maximum, but there is a pronounced defi- ciency of atoms on the low-velocity side and an ob- servable excess of atoms on the high-velocity side. It if the velocity distribution had undergo a velocity-dependent scattering which was not serious enough to shift the maximum of the distribution Run 31 illustrates the effect of a deep slit on the velocity distribution. These slits were made of copper trips which were 0.317 cm thick. In this case, the entire distribution has been shifted in the high velocity direction. It was also found that when the 0.003-cm or 0. 004-cm steel shims which formed the orifice from which the beams effused from ovens like those shown in Fig 3 were omitted, so that the orifice was determined by the knife edges of the copper strips, the velocity FIG. 5. Typical thallium velocity distributions. The data were taken with thin oven slits at vapor pressures given in Table II