ON THE EVOLUTION OF THE STARS? 
By C. G. ABBot 
a 
[With 6 plates] 
1. There are 92 chemical elements, beginning with hydrogen ana 
ending with uranium. Oxygen is the eighth, iron the twenty-sixth, 
silver the forty-seventh, gold the seventy-ninth, and radium the 
eighty-eighth. Nearly all of them are found on the earth, and a great 
many of them in the sun and stars. There are many ways of identi- 
fying them on the earth, but only one way in the sun and stars. The 
spectroscope reveals the signs of the chemical elements in the light 
of the heavenly bodies. 
The spectrum is a band of beauty. Its colors blend from violet 
through indigo, blue, green, yellow, orange, to red most charmingly. 
But in the spectrum of light from the sun, or from the stars, one sees 
the band of color shot across with many dark lines. It is these lines 
which tell the chemical story. 
Here are the lines of green color that iron gives when heated in 
the electric arc. Here are the dark lines that are produced when 
light shines through iron vapor. Here are those very lines in the 
spectrum of the sun. Hence, there is iron in the sun. The proof is 
just as plain as that which tells us that ages ago a queer-toed animal 
walked in the mud of Massachusetts, for we have found fossils of 
his tracks. 
In such ways the spectroscope has told us that all of the stars are 
composed of the same chemical elements as our earth. This is the 
first conclusion in our study of stellar evolution. The chemical com- 
position of all parts of the universe, however distant, is the same. 
2. The atoms of the 92 chemical elements are made up of two 
and only two ingredients. These fundamentals are called the protons 
and the electrons. The protons are unit positive electrical charges. 
The electrons are unit negative charges exactly equal but opposite in 
nature to the protons. 
In a single atom of hydrogen there are one proton and one electron. 
In a single atom of oxygen there are 16 of each, and in heavier atoms 
many more. This is the way they are arranged: The protons and 
1 Lecture delivered at Columbia University, July 15, 1926. 
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