Page:Sir William Herschel, his life and works (1881).djvu/211

Rh rank indeed, and I trust that the brief summaries, which alone can be given here, will have made this plain.

We may conclude from the time expended, the elaborate nature of the experiments involved, and the character of the papers devoted to their consideration, that the portion of researches in physics which interested him to the greatest degree, was the investigation of the optical phenomena known as  rings. In 1792 he obtained the two object-glasses of, which were in the possession of the Royal Society, for the purpose of repeating experiments, and in 1810 he read the last of his three papers on the subject.

Sir had given some of his most vigorous efforts to the study of the phenomena of interference of light, which are exemplified in the colors of thin and of thick plates. The colors of thin plates are most conveniently studied in the regular form which they present when produced by a thin plate of air, limited on one side by a plane