ASTRONOMY: H. N. RUSSELL 
413 
brightness of the giant stars of all spectral types has found a simple 
explanation. 
If the conclusion that the luminosity of a giant star is a function of its 
mass, but not of its temperature or age, is confirmed, and the nature of 
the function fixed by observation, the problem of determining the masses 
of stars which are not double will in many cases be solved. 
Jeans, discussing the problem of the figures of equilibrium of a rotat- 
ing mass of compressible fluid, has already reached conclusions which not 
only bear upon the origin of double stars, but have suggested an entirely 
new and very stimulating conception of the nature of spiral nebulae, as 
huge rotating masses of gas, which, becoming unstable at the edge under 
the influence of their own rotation and the attraction of the neighboring 
stars, throw off matter from their periphery in streams of such enormous 
size that they may divide into 'nuclei' large enough to form ordinary 
stars upon condensation. 
In the field of galactic astronomy, Schwarzschild^^ has developed 
powerful methods for handling the statistical material which must be 
our main guide, and Jeans^^ and Eddington^^ have shown that 'star 
streaming' demands no unknown forces for its explanation, but is prob- 
ably interpretable dynamically, as a property of a system of stars in 
motion under their own gravitation — although the existence of ' stream- 
ing' appears to indicate that the galactic system is not in a ' steady state. ^ 
Eddington^^ has shown that the similarity of distribution of the stars in 
different globular clusters presents a problem by no means simple, though 
of much interest. 
Almost the whole of this work has appeared within the last three years, 
and further notable advances may be anticipated. Indeed, almost as 
these words are written, comes the first installment of an important 
paper by Eddington^^ on the oscillations of a gaseous star, which may 
afford the long-sought solution of the problem of Cepheid variation. 
Among other specific problems awaiting discussion may be mentioned 
the question whether the tidal interaction of two compressible and 
slowly condensing bodies can cause an originally small eccentricity to 
increase to the very large values which are found in many visual binaries, 
and some spectroscopic binaries as well; and, if this proves to be impos- 
sible, how the systems in question can have originated the origin and 
laws of the complicated changes which occur in the periods of many 
eclipsing binaries; and the equilibrium and motions of the constituent 
parts of planetary and spiral nebulae. 
Mention should also be made of the work of Nicholson*^ on the 
interpretation of unknown lines in the spectra of nebulae and of the 
