SECRETARY’S REPORT 83 
may reveal other related effects of energy absorption in the upper 
atmosphere. By calculating theoretical spectra for early-type stars, 
and calculating the blanketing effects in the solar atmosphere, Dr. Max 
Krook has been investigating the propagation of disturbances through 
a stellar atmosphere, and associated phenomena such as radio fre- 
quency emission and the acceleration of charged particles. With Dr. 
J. C. Pecker, of the Paris Observatory, he plans to apply a method 
he has devised for solving equations in nongray atmospheres. Dr. 
Krook continues his efforts to obtain exact numerical solutions of non- 
linear kinetic equations for the case of shear flow with heat transfer, 
and to determine a wide range of values of the Mach number, the 
Knudsen number, and the temperature ratio. Such solutions will 
bear on the validity of various approximation procedures for solving 
Boltzmann equations. The formal mathematical analysis of these and 
related problems was completed this year. 
Dr. Charles Whitney continued the investigation of gas-dynamical 
problems associated with the solar atmosphere and the atmospheres of 
variable stars. He has formulated the equations appropriate to the 
solar atmosphere; initial integrations have been performed on an 
electronic computer, and the stability of the equation is being investi- 
gated. From studying variable stars of small amplitude and their 
pulsational instability, he hopes to determine the exact limits to the 
domains of variable stars, and the properties of variables near these 
limits. Spectrographic data on cepheid variables will furnish an 
empirical foundation for subsequent investigations of the gas dy- 
namics of variable stars. Dr. Whitney is also testing the theory that 
the ionization zone is the seat of pulsational instability. During the 
year he completed a detailed theoretical explanation of the period- 
luminosity relationship, which has significance for problems of stellar 
evolution and the size of the galaxy. 
Dr. Alan S. Meltzer, before he left the Observatory in September 
1957, carried out studies of solar line profiles and the variation of 
Doppler half-widths of lines with varying atomic weights, to deter- 
mine whether the broadening mechanism is kinetic temperature or 
turbulence. The atomic-weight dependence of the Doppler broaden- 
ing of these lines corresponds to a kinetic temperature of about 10,000° 
K, a value substantially higher than that predicted by accepted 
theories of the solar atmosphere. 
Upper atmosphere.—Dr. Theodore E. Sterne has been studying the 
inferential methods used in evaluating observational data, and the 
probable degree of validity of the resulting conclusions—one of the 
most important problems in astronomy today. He has developed 
methods based on celestial mechanics for inferring the density of the 
upper atmosphere from the motions of artificial earth satellites; 
