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Life and Works
visible to the naked eye in the years 1863 to 1866. He examined the nature of the spectrum of each of the larger stars, and found that these stars could be arranged in three general classes or types. His results have been verified and extended by other astronomers, and his classification has been generally accepted. According to Secchi, the lucid stars may be separated into three groups, distinguished by marked differences in their spectra. Secchi's Type I. contains stars whose spectra are like those of Sirius, Procyon, and α Lyræ; his Type II. stars like Arcturus and Aldebaran; his Type III. stars like α Orionis.
Herschel also made some trials in this direction. In the Philosophical Transactions for 1814 (p. 264), he says:
"By some experiments on the light of a few of the stars of the first magnitude, made in 1798, by a prism applied to the eye-glasses of my reflectors, adjustable to any angle and to any direction, I had the following analyses:
"The light of Sirius consists of red, orange, yellow, green, blue, purple, and violet, α Orionis contains the
