Curves of Growth for the a Dwarfs γ Geminorum and Sirius.

Curves of growth are derived for `y Geminorum and Sirius from plates taken at the McDonald and Mount Wilson observatories. The excitation temperature of these stars turns out to be about 60000 and the ionization temperature about 8700°, as compared with an effective temperature of 10,000°. The electron pressure derived from the broadening of the hydrogen lines is about 1.2 X 102 dynes, as com- pared with about 7 X 102 dynes predicted by theory. If iron is half-ionized in the sun, the amount of metallic vapor above the photosphere of the sun is about twenty times the amount above the photosphere of Sirius. This resuk is in good agreement with that obtained by Adams and Russell in 1928. The amount of hydrogen in the A dwarfs is found to be about a thousand times the amount of iron (by weight)