; -1; Sc, Y+ gives the maximum 2 ? ; -3 Maximum ill determined, but probably due to Y+ 3 ? -1 Remark in Rowland:--in zircon but not in Zr Ba 1 none Unblended CONSISTENCY OF RESULTS The preceding tabulation summarizes the present state of the observational material bearing on the positions of the maxima of absorption lines. The comparison with theory is an important and difficult problem. The theoretical formulae contain as variables the temperature and the pressure; and the [Pg 131] fractional concentration, , is very sensitive to changes in both these variables. It would therefore be possible to satisfy almost any observations by varying the two quantities jointly; but this procedure would furnish no useful test of the theory. The test made in the present chapter will involve the calculation of the temperature scale, with the partial electron pressure, , assumed constant. Figure 8 Reproduced from H.C. 256, 1924. Comparison between observation and ionization theory for the hotter stars. The observations are contained in the upper part of the diagram, and the theoretical curves (based on a partial electron pressure are given in the lower part of the figure. For the upper half, ordinates are the observed intensities contained in Table XIX; abscissae are spectral classes from the Draper Catalogue. In the lower part of the figure, ordinates are logarithms of computed fractional concentrations; abscissae are temperatures in thousands of degrees. The abscissae of the upper and lower diagrams have been adjusted so that the observed and computed maxima coincide, thus forming a preliminary temperature scale. It is certain that this condition is not satisfied in practice, and a more rigorous treatment, which allows for the differences in partial electron pressure, is contained in the chapter that follows. But with the object of examining the consistency of the derived temperature scale, the present test is made under the assumption that the partial electron pressure is constant and equal to about [Pg 132] . The resulting scale of temperatures for the reversing layers of the corresponding classes is contained in the table that follows. Successive columns contain the element that is utilized, the spectral class at which its lines attain maximum, and the corresponding temperature derived from the equations of Chapter VII. Element Maximum Temperature Element Maximum Temperature He+ 35000° Ti 3500° Si+++ 25000 Mn 5000 Si++ 18000 Fe 5000 He 10000 V 3500 C+ 16000 Cr 3500 Si+ 11000 Sr+ 6000 H 10000 Ba+ None 5500 *Zn 8000 Ca 4500 *Ca+ 6000 * Estimates by Menzel, H. C. 258, 1924. FOOTNOTES: [403] Payne, H. C. 256, 263, 1924. [404] Menzel, H. C. 258, 1924. [405] Harper and Young, Pub. Dom. Ap. Obs., 3, 3, 1925. [406] Chapter X, p. 142. [407] Menzel, H. C. 258, 1924. [Pg 133] CHAPTER IX THE IONIZATION TEMPERATURE SCALE