Inventions in the Century

by William Henry Doolittle

Newton in the next century, with the prism, decomposed light, and in a darkened chamber reproduced all the colours and tints of the rainbow. But there were dark lines in that beam of broken sunlight which Newton did not notice.

It was left to Joseph von Fraunhofer, a German optician, and to the 19th century, and nearly one hundred years after Newton’s experiments with the prism, to discover, with finer prisms that he had made, some 590 of these black lines crossing the solar spectrum. What they were he did not know, but conjectured that they were caused by something which existed in the sun and stars and not in our air. But from that time they were called Fraunhofer’s dark lines.

From the vantage ground of these developments we are now enabled to step to that mountain peak of discovery from which the sun and stars were looked into, their elements portrayed, their very motions determined, and their brotherhood with the earth, in substance, ascertained.

The great discovery of the cause of Fraunhofer’s dark bands in the broken sunlight was made by Gustave Robert Kirchoff, a German physician, in his laboratory in Heidelberg, in 1860, in conjunction with his fellow worker, Robert Bunsen.

Kirchoff happened to let a solar ray pass through a flame coloured with sodium, and through a prism, so that the spectrum of the sun and the flame fell one upon another. It was expected that the well known yellow line of sodium would come out in the solar spectrum, but it was just the opposite that took place. Where the bright yellow line should have fallen appeared a dark line.

With this observation was coupled the reflection that heat passes from a body of a higher temperature to one of a lower, and not inversely. Experiments followed: iron, sodium, copper, etc., were heated to incandescence and their colours prismatically separated. These were transversed with the same colours of other heated bodies, and the latter were absorbed and rendered black. Kirchoff then announced his law that all bodies absorb chiefly those colours which they themselves emit. Therefore these vapours of the sun which were rendered in black lines were so produced by crossing terrestrial vapors of the same nature.

Thus by the prism and the blowpipe were the same substances found in the sun, the stars, and the earth. The elements of every substance submitted to the process were analysed, and many secrets in the universe of matter were revealed.

Young, of America, invented a splendid combination of spectroscope and telescope, and Huggins of England was the first to establish by spectrum analysis the approach and retreat of the stars.

It was prior to this time that those wonderful discoveries and labours were made which developed the true nature of heat, which demonstrated the kinship and correlation of the forces of Nature, their conservation, or property of being converted one into another, and the indestructibility of matter, of which force is but another name.

The first demonstrations as to the nature of heat were given by the American Count Rumford, and then by Sir Humphry Davy, just at the close of the 18th century, and then followed in this the brilliant labours and discoveries of Mayer and Helmholtz of Germany, Colding of Denmark, and Joule, Grove, Faraday, Sir William Thomson of England, of Henry, Le Conte and Martin of America, as to the correlation and convertibility of all the forces.