In this third paper: the 1962 11e3 Scale of T emperatures is evaluated both as to its pre cision a nd its devi ation s from the thermodynamic K elvin Scale. Variou s ther modynamic quantities of If e3 con sistent with the 1962 11 e 3 Scale are derived and listed. The correct ion to a n observed vapor pressure for small amounts of 11e' is di scussed a nd tabulated . A descrip tion is given of the method of m llitiple variable least squares an alys is used for d eriving the final scale equ at ion and for re-analys is of isotherm dat a . F inally the present status of the 1962 IIe 3 Scale is discussed a long wit h som e con sideration s for the future. One factor in evaluating the 1962 H e 3 Scale is the fit of the input vapor-pressure data of Part I [46] to the Scale. Figure 1 and table 1 of Part II [6] show the deviations of the observed da ta from the final scale as T 62 (P 3) -T 5s(P 4)' The symbol T 62 is the temperature on t.he 1962 He 3 Scale corresponding to a He 3 vapor pressure, P 3, while T 58 is the tempera ture on the 1958 He 4 Scale [2] corresponding to the experimentally determined isothermal He 4 vapor pressure, P 4 • The standard deviation of the data from the scale is 0.25 mdeg and the maximum deviation over the full range is 0.6 mdeg. The data may not scat,ter completely randomly. For example, the data points just below 2 O K are all b elow the 1958 He 4 Scale and the point.s just above 2 O K are all above the 1958 He 4 Scale. H ence, if one wished to obtain the vapor pressure of H e 3 which is most probably isothermal with a given H e 4 vapor pressure, ;t slightly better value (in terms of consistency with the observed data) may be obtained by drawing a smooth curve through these data points or by using direct interpolation equations as discussed in Part I. However, the overall fit of the Scale to the inpu t data is very satisfactory in comparison with the errors of measurement of the two vapor pressures.I Much of the maierial in this paper III has been included ill a review chapter [52] on the development of ih e seale., IYork performed und er ihe auspices of t he U. S. Atomic Energy Commission . 567 Fit of the Experimental Thermodynamic Equation (ETE) ScaleBelow 0.9 O K the 1962 He 3 Scale was evaluated by examining its fit to the ETE Scale described in Part II. The ETE Scale is defined by a linear equation fitted to an empirical function, FX(P3,T), of H e 3 vapor pressure and temperature,As shown by the full line curve in figure 1 of P art II, temperatures calculated from eq (1) are in good agreement with the 1962 He 3 Scale; nowhere b elow 2 O K do the scales differ by more than 0.4 mdeg. the 1962 He 3 Scale, defined by eq (9b) of P art II, is therefore in effect an ETE scale from 0.2 to 2° and an empirical scale above 2 O K.The effect of possible errors in the various terms of the equation for the ETE scale, over the temperature range from 0.2 to 1.0 O K, should also be considered in evaluating the 1962 H e 3 Scale. The ETE scale was obtained from a least squares fit of the H e 3 -H e 4 vap...

Thermomolecular pressure ratios of He 3 have been measured for a tube extending from room temperature to a bulb at 2°K. The results agree within experimental accuracy with He 4 ratios calculated from the Weber-Schmidt equation. Detailed calculations from this equation are given. Limitations of the equation due to large deviations from ideal viscosity behavior in the liquid helium range are discussed.

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The detail ed tables of t he 1962 I-l e3 Scale of T emperatures are presented. The vapor press ure of H e~ is tabu lated i n steps of 1 mill idegree from 0.2 to 3.324 oK, the critical temperature. A table giving t emperature, to 0.1 milli dE'gree, as a fu nction of press ure is included, as well as t he t emperat ure derivative of t he vapor pressure.

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