Henry Norris Russell

The Arc and Spark Spectra of Gadolinium

Analyses based on wave-numbers and intensities have led to the classification of 1177 lines of Gd ii, and 1217 of Gd i. The percentages of the stronger lines which have been classified are respectively 77 and 90; of all lines 45 and 40. Almost all lines of astrophysical interest are included.All the identifiable terms are derived from the ground-state 8S° of the triply ionized atom. A complete analysis will probably be very difficult. The multiplets are remarkably regular for so high an atomic number. Intercombinations are numerous and strong, and often occur between terms differing widely in multiplicity and type. Terms of multiplicity 11 are present in Gd i and account for some of the strongest lines.

The Atmosphere of Venus

I would l i k e t o thank those p a r t i c i p a n t s who helped i n c o r r e c t i n g t h e i r e d i t e d t a l k o r t h e i r comments from t h e f l o o r , and I apologize t o t hose who d i d n o t check t h e i r c o n t r i b u t i o n i f t h e e d i t i n g a f f e c t e d t h e i n tended meaning. I t tu rned out t o b e p o s s i b l e t o a s s o c i a t e a name w i t h each comment from t h e f l o o r ; t h e a f f i l i a t i o n s of a l l p a r t i c i p a n t s a r e l i s t e d a t t h e end of t h e proceedings . However t h e i r r e p r e s s i b l e D r . J ones , who i s known t o have a f f i l i a t i o n w i t h a number of i n s t i t u t i o n s , p r e f e r r e d n o t t o r e v e a l h i s address . I would a l s o l i k e t o thank L i sa Nazarenko, Car l Codan and David Rosen f o r he lp ing t o organize t h e conference and David Ghesquiere f o r drawing many of t h e f i g u r e s . And I am p a r t i c u l a r l y g r a t e f u l t o L i sa , who p u t t o g e t h e r t h e s e proceedings inc lud ing a l l t h e typ ing and s p l i c i n g i n of f i g u r e s .

Estimation of Ionization Potentials by Comparison with Neighboring Elements

If a spectrum contains an unperturbed series of at least three members, the ionization potential can be found with fair accuracy from its limit. If but two members are available, serious errors occur if the Ritz correction is ignored. This correction can often be closely estimated by comparison with elements of neighboring atomic numbers. This method is familiar, but published estimates have not been made on a uniform system. Such estimates for spark spectra from Ca ii to Zn ii give ionization potentials differing from a smooth formula by ±0.02 volt, while the differences in the three cases where the Ritz correction was not applied, average ±0.39 volt.

THE DISTRIBUTION OF DENSITY WITHIN THE STARS

To find out anything about the distribution of matter inside a star demands the use of an “analytical boring machine ”-as Eddington says-and it is only under rather special circumstances that such a machine can get to work. Three different methods, however, have proved available, not merely “in principle’’ but in practical application. Two of these are of a “classical” nature, and depend essentially upon gravitation; the third involves modern astrophysics. I will speak of this first,-briefly, since it does not really come under our morning’s title. The equilibrium of the gaseous matter inside a star is now pretty well understood. At least, almost all the principal investigators have been led by their researches to agree upon the main principles. The principal observable characteristics of a star are its mass, its radius, and its luminosity. If we know these, we can find the value of gravity at its surface, the surface temperature, and the rate at which heat flows out per unit area. We can then work inward from the surface, calculating the density, pressure and temperature in deeper layers, provided that we know two things about the material, the mean molceular weight and the opacity, which determines the rate of rise of temperature with depth. Fortunately for us, both these quantities, under stellar conditions, depend mainly on the percentage of hydrogen which is present. The relative proportions of other kinds of atoms do not matter much (though helium has some influence). Chandrasekhar has developed an effective way of doing this, by which one can figure out with good approximation how deep we would have to go to leave behind us a given fraction (say one-tenth) of the whole mass of the star. The remaining 90 per cent of the mass will then be enclosed in a sphere whose radius is a given fraction (which Chandrasekhar calls E*) of the whole star. For a star of uniform density, E* would be 0.965. Smaller values indicate that the density increases toward the center. Applying his method to Capella, Chandrasekhar finds that if there is no hydrogen at all inside, 4* = 0.68, indicating a small central condensation. With 30 per cent of hydrogen it drops to 0.50; with 80 per

ON THE NAVIGATION OF AIRPLANES

i. Introductory. The present paper contains an account of investigations on the determination of the geographical positions of airplanes by means of sextant observations made during flight. These studies were made under the authority of the Division of Science and Research of the Bureau of Aircraft Production (in whose service the writer was at that time engaged as an engineer), and the present account is published by permission of Colonel Millikan, who was at that time in command of the Division. Most of the work was done at Langley Field, Hampton, Va., where every facility was afforded by the Commanding Officer, Major Howard, and those subordinate to him in authority. Observations in naval seaplanes were also secured through the courtesy of the Commanding Officer of the Naval Air Station at Norfolk. In the conduct of the observations, the writer received assistance of the greatest importance from Captain D. L. Webster (now Professor at the Massachusetts Institute of Technology), to whose skill in piloting a great part of the success of the investigation is due; from Mr. J. P. Ault, navigating officer of the non-magnetic vessel Carnegie, who was assigned to this work by the Department of Terrestrial Magnetism of the Carnegie Institution of Washington, and brought to it exceptional skill and experience in navigation at sea; and from Professor R. W. Willson of Harvard, whose bubble telescope proved to afford the best solution of the problem. Valuable aid and cordial interest in the work were also shown by many pilots and other officers at Langley Field and the Naval Air Station, to all of whom the writer offers his hearty thanks.