Page:Popular Science Monthly Volume 67.djvu/292

286 it undesirable to follow the matter further at that time.

Professor Young's expedition to Wyoming in the summer of 1872, to utilize the advantages of an altitude of over eight thousand feet, added a hundred chromospheric lines to the list of 170 which he had observed at Dartmouth.

It may be mentioned that this list has been but slightly enlarged since that date, and that by Professor Young himself at Princeton. In 1876, with the first grating spectroscope used in astronomical work, he made the pioneer measurements of the rotation of the sun from the relative displacements of lines on the approaching and receding limbs. We are indebted to him for important observations on the spectrum of sun-spots, made after his