First Scientific Uses

Spectrographs using “trains” of prisms will substantially disperse the light being studied, enabling researchers to see greater detail; unfortunately, prisms also absorb too much light. As a result, from around 1860 on, gratings were considered a more efficient solution for scientific investigations.

Lewis M. Rutherfurd’s ruling engine, ca 1872

The observation of spectra with spectroscopes was particularly stimulated by the work of Gustav Kirchoff and Robert Bunsen. In 1859, they described the three fundamental laws governing the emission and absorption of spectral lines in gases: rules that would become the backbone of chemical analysis. Their findings encouraged Lewis M. Rutherfurd to make ruling engines in order to improve the efficiency of spectral investigations. He enjoyed some success and, by 1872, his gratings had more than 15,000 lines per centimetre (6,000 lines per inch). He gave his gratings to friends, as well as to scientists whom he knew would make good use of them. Rutherfurd’s gratings were considered the best available — certainly for the price: free! Nobert’s gratings were only occasionally superior to Rutherfurd’s and were difficult and expensive to acquire.

In astronomy, spectroscopy became a key tool to understanding the physical make-up of stars and how they evolved. We can’t visit stars, but we can see great detail in our own star, the Sun. Using gratings, literally thousands of absorption lines were observed in the solar spectrum. The gases, and the conditions that gave rise to them were, with the exception of hydrogen, carbon, nitrogen and oxygen, a mystery. Over the decades, the origins of the lines were gradually discovered and interpreted by physicists and chemists. Mystery lines; including emission lines were still observed, however, in some stars, nebulae and galaxies. The movements of spectral lines — so-called “Doppler shifts” — revealed stars orbiting each other and enabled us to measure the physical properties of star systems. Through spectral analysis such as this, we gradually began to learn more about the evolution of stars and other astronomical bodies.