Howard Donald Books

In recent years, with the widespread interest in the control of thermonuclear energy, there has been a great rise in the study of highly ionized gases, or plasmas. Within this area of study there have been broadly two avenues of approach: the work of the plasma physicist (and related workers) and the work of the astrophysicist, who has been observing and interpreting similar phenomena in stars and nebulae.

Astrophysical analysis and interpretation (by spectroscopy) began with pioneering work upon hydrogen. This work was extended later into the study of many types of physical processes in highly ionized gases, including both radiative and collisional interactions with atoms other than hydrogen. These studies, which have hitherto appeared only in periodicals and have not been generally available, are now recognized as
basic to many areas of physics and geophysics, and their general theory is applicable to many problems other than those of nebulae.

Professor Menzel, one of the foremost contributors in this field, has selected 30 such papers with the assistance of Dr. L. H. Aller. They include a paper on the theory of hydrogenic spectra, and 18 papers upon the physical processes in gaseous nebulae, covering problems of radiation and radiative transfer, the Balmer decrement, electron temperatures, excitation, electron densities, spectrophotometry, statistical equilibrium of neutral helium, the abundance of 0 III, fluorescence in high-excitation planetaries, and the chemical composition of planetary nebulae. The third portion of the book is devoted to 10 papers on the interpretation of nebular spectra, covering electron velocity distribution, multiplet intensities, spectrophotometry, thermal effects, and various spectral analyses. The final paper is concerned with the intensities of "forbidden" spectral lines.