He also produced observations in a publication on star colours entitled "Sidereal Chromatics" in 1864, which attempted to explain their nature, the effects of the Earth's atmosphere, and the possibility of change in colour due to Doppler Shift. While his premise proved ultimately wrong, he discussed and created a summary on observing star colours of many double stars under his so-called Hartwell Experiment. Some of his ideas continued to be promoted into the early 20th century, but were mostly then rejected by the overwhelming evidence from astronomical spectroscopy.