200-INCH HALE TELESCOPE—HUBBLE 181 
The length over which a spectrum can be spread, and still remain 
bright enough to be photographed, depends upon the brightness of 
the object. The sun has been spread out over a spectrum about 50 
feet long from red to violet; the brightest stars, over about 3 feet, 
and the faintest naked-eye stars over about 1 foot. The shortest 
spectra giving useful information are about one-tenth of an inch long, 
and have been obtained from stars and nebulae about a hundred 
thousand times fainter than the faintest naked-eye stars. With the 
200-inch, all the stellar and nebular spectra can be lengthened about 
four times, and consequently the analysis can be carried out much 
more precisely than was hitherto possible. 
One new field, now faintly glimpsed, can be explored rather fully. 
The important data are the relative abundances of the different chem- 
ical elements in different kinds of stars. These data are derived from 
the comparative study of the different stations (or lines) due to differ- 
ent chemical elements in a spectrum, and require the longest practical 
spectra (the highest possible dispersion) for adequate analysis. 
There is reason to believe that more than 99 percent of the atoms 
in the universe are hydrogen. Even by weight, hydrogen, with the 
simplest and lightest of all atoms, probably contributes a large frac- 
tion of the total matter in the universe. There are insistent sugges- 
tions that the relative abundance of hydrogen varies considerably 
from star to star. There is also some reason to suppose that the rela- 
tive abundance of other elements does not vary widely in the stars, 
although the physical conditions of the stars do vary widely (from 
giants to dwarfs, from hot blue stars to cool red stars). The supposi- 
tion rests mainly on negative evidence and requires further study 
with powerful instruments. 
It is believed that the 200-inch alone can adequately explore this 
field, now dimly outlined with existing telescopes. What is now sug- 
gested by analysis of three or four of the very brightest stars can be 
critically tested in these objects, and the study can be extended in a 
comparable way over a large sample collection of stars in general. 
We cannot predict the final results of the exploration. They may 
represent the next major chapter in the development of our knowledge 
of the universe, or they may prove to be relatively trivial. But the 
unexplored field looms as a challenge, and the challenge will be met. 
The data are immensely important because they bear directly on 
two very fundamental problems, namely, the source of stellar energy 
and the origin of chemical elements. 
Geologists, studying the history of the earth’s surface, assure us 
that the sun has been pouring out energy at a fairly constant rate 
over the last several hundred million years at least. Possible sources 
for the unfailing supply were not only unknown but were unimagined, 
