Donald H. Menzel

Generalized Tables for the Calculation of Dipole Transition Probabilities.

Abstract : Calculation of transition probabilities or oscillator strengths for allowed trasitions proceeds in two steps: calculation of the dipolemoment matrix in a simple coupling scheme (usually LS-coupling) followed by transformation of this matrix to the energy scheme. Though the oscillator strength for and transition is proportional to the square of a matrix element, the transformation step requires absolute values, including signs (=). Existing tables of line and multiplet strengths omit these signs, and hence are useful only when the atomic states are nearly LS-coupling states - ofter a poor approximation. (Author)

THE ATMOSPHERE OF MARS

Martian atmosphere examined through its redness, its albedo and its surface markings, noting also the composition of its two layers of particulate matter

ON THE OBLITERATION OF STRONG FRAUNHOFER LINES BY ELECTRON SCATTERING IN THE SOLAR CORONA

The invisibility of Fraunhofer lines in the inner corona at solar eclipses first indicated the very high temperatures present there. Scattering by fast electrons presumably washes out the lines. In this article we emphasize that the evidence is still unclear whether the strongest photospheric absorption lines appear as wide depressions in the K corona, and we re-examine data pertinent to the discussion.

A RELATIONSHIP BETWEEN FLARES AND LOOP PROMINENCES

Just over one hundred years ago, Carrington made the first observation of a solar flare.1 On September 1, 1859, while making his customary observations of sunspots on an eleven-inch projected image of the sun, he saw two brilliant crescents develop simultaneously in white light over a large and complex sunspot group. Startled, he thought at first that a ray of light must have penetrated the intensity-reducing screen attached to his object lens, but after making minor test movements with his telescope he realized that something unusual was happening on the sun and ran to get a confirming witness. By the time he returned, only a minute or two later, the crescents (A and B in Fig. 1) had dis-

Torsional Oscillations and Solar Magnetic Fields

Torsional magneto-mechanical oscillations of finite amplitude in an idealized non-uniformly rotating star that possesses a poloidal magnetic field are governed, in a first approximation, by a pair of linear wave equations. The approximation is valid if the rotational energy and the magnetic energy are small compared with the gravitational energy. Making various assumptions about the form of the poloidal field, we derive numerical estimates for the period of the fundamental mode (table 1), and discuss the results as they relate to the problem of solar variability.

Turbulence, kinetic temperature, and electron temperature in stellar atmospheres

Abstract The phenomenological use of the term “astronomical turbulence” is reviewed and earlier conclusions that the physical nature of the phenomenon is more likely anisotropic mass-motion, or jet-prominences, than the customary aerodynamic turbulence are restated. The primary problem under such conditions is the relative importance of mechanical energy-transport and momentum transport in perturbing the structure of the atmosphere. The problem of the difference between kinetic temperatures of the atoms and electrons is treated, and it is concluded that the difference is negligible in those parts of the stellar atmosphere which are in a statistically-steady state.

THE SUN'S MAGNETIC FIELD AND THE STABILITY OF SOLAR MARKINGS,

Abstract : This paper relates to the interpretation of photographs taken at the Lockheed Solar Observatory with an H-alpha filter having a pass band of 0.5 Angstroms. Photographs taken at the line center refer to higher atmospheric levels than do those taken in the wings. The program of solar photography at Lockheed has featured the taking of records in rapid sequence at 10 sec intervals. Records taken approximately 0.5 Angstroms to the red or violet of the line center are relatively free from the complex bright and dark plages characteristic of chromospheric and prominence activity. (Author)

The Escape of Planetary Atmospheres

The problem of escape of atmospheres from the Moon and planets has roots deep in ancient history. Many of the great philosophers of the past regarded the Earth’s atmosphere as a medium extending to infinity, with a stationary Earth imbedded at the center. Indeed, it was this concept that led Ptolemy, among many others, to conclude that the Earth could not be moving, for otherwise it would be subject to a gale-force wind caused by its own motion. This idea fostered many of the early stories of interplanetary visitations. Lucian, for example, writing in the second century A.D., has his Icarome nippus fly to the Moon and beyond by means of wings attached to his body.

Further Identifications of Nebular Lines

whereby complex nuclei are built up by the addition of neutrons to lighter nuclei. It has in the past been assumed that only a negligible fraction of the atoms in interstellar space were in excited states. This depended on the assumption that the excitation probability was proportional to the radiant energy-density while the return to the normal state was rapid and spontaneous. It should be pointed out, however, that the metastability of certain excited states may be so strong that the spontaneous transition coefficient may not govern the equilibrium. Such states will be reached by double processes, and return to the normal state will also take place largely by double processes involving radiation. Atoms can exist in such metastable states in fractions

ANNIHILATION OF MATTER AS THE SOURCE OF STELLAR ENERGY

defy all attempts at accurate delineation. Logic recognizes two types of reasoning: deductive and inductive. In the one case, we start from certain assumptions or postulates and develop a proof along purely formal lines. In the other, we start from certain observed facts and reason backward to the underlying cause. These have been called, respectively, the mathematical and physical methods, if for no other reason than that the mathematician often apologizes when circumstances force him to employ inductive reasoning and that the physicist, even the mathematical physicist, apologizes when he finds it necessary to rely upon postulate and formal deduction rather than upon his experiments. It must be recognized that neither method is entirely satisfactory. The validity of a deductive proof lies in the validity of the fundamental postulates as well as in the accuracy of the reasoning. Mathematics is an ideal machine, but the quality of its products can never exceed the quality of the raw material. The chief danger of the inductive method was clearly shown by Poincare, who said in effect : Any experimental fact or set of experimental facts can be accounted for by an infinity of hypotheses. The physicist customarily adopts the simplest, and again, since relative simplicity is a matter of human opinion, it is not surprising that disagreements frequently occur. The past several years have brought about a remarkable change in the character of physical investigations, especially in the field of atomic physics. True, the scientist still insists upon