How the star-light tells us what the stars are made of

"This picture shows us how the spectroscope is used to enable men to catch the light of a star, and, by passing it through a glass prism, to break up the light into various colours. As different metals give us different colours, we can in this way tell what the stars are made of. This picture does not show the whole spectroscope, but illustrated the principle."

Source: "The Children's Encyclopaedia" (1910)

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