ASTRONOMY IN A WORLD AT WAR—DOUGLAS 161 
these elements compose all stellar bodies as well as all things ter- 
restrial, their synthesis is a cosmic problem. They find that such 
tremendous extremes of high temperature and high density would be 
required that it is necessary to suppose that all the matter of the 
known universe was once confined to a volume of radius only about 
twenty times that of the solar system. Such a sphere drawn around 
our sun as center does not now contain a single other star. Yet into 
such a volume there may once have been packed not’ only all the 
thousand million stars of our own galaxy, but all the millions of 
other galaxies. This is indeed a picture reminiscent of the “giant 
molecule” of Lemaitre. Since stars and galaxies are not now thus 
packed, expansion must have taken place some time very long ago. 
The present rate of expansion is such that galactic distances are 
doubled every 1,800 million years. This gives the time elapsed, since 
the expansion began, as several thousand million years which is in 
satisfactory accord with the age of the earth as determined by other 
physical lines of approach and regarded necessarily as a lower limit 
for the age of the universe. 
The last chapter on these cosmological problems is not yet written— 
indeed there may well be many chapters yet to come and still no last 
chapter in sight. It is the glory of the quest that as men seek the 
unexplored horizon the margin fades forever and forever as they 
move. 
V 
An investigation of very recent date has led to positive conclusions 
about planetlike bodies associated with stars other than our sun. 
There is strong evidence for this in the case of 61 Cygni and 70 
Ophiuchi. This may be the beginning of a new search and a new 
certainty in a field of astronomy hitherto theoretical and speculative. 
Already several astronomers on two continents are studying the im- 
plications. 
Another astrophysical problem that has been worked upon with 
considerable success during these war years, is the old backlog prob- 
lem since 1869 of the solar corona. At Uppsala, Edlén has been 
examining the X-ray and ultraviolet spectra of some very highly ion- 
ized atoms, and a year ago his 1942 paper was received in England and 
also in the United States of America. He uses his laboratory data as 
basis for calculation of forbidden lines and altogether he identifies 17 
coronal lines with lines of Fe X, XI, XIII, XIV, XV, Ni XII, XIII, 
XV, XVI, Ca XII, XIII, A X; and two other lines less certainly with 
Ca XV and A XIV. The ionization potentials required to produce 
such atoms are very high, actually 233 volts for Fe X, 655 volts for 
Ca XIII, and at first this seemed to offer an insuperable obstacle to 
