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of William Herschel.
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same colors, but the red is more intense, and the orange and yellow are less copious in proportion than they are in Sirius. Procyon contains all the colors, but proportionately more blue and purple than Sirius. Arcturus contains more red and orange, and less yellow in proportion than Sirius. Aldebaran contains much orange and very little yellow, α Lyræ contains much yellow, green, blue, and purple."
Here the essential peculiarities of the spectrum of each of the stars investigated by Herschel is pointed out, and if we were to use his observations alone to classify these stars into types, we should put Sirius and Procyon into one type of stars which have "all the colors" in their spectra; Arcturus and Aldebaran would represent another group of stars, with a deficiency of yellow and an excess of orange and red in the spectrum; and α Orionis would stand as a type of those stars with an excess of red and a deficiency of orange, α Lyræ would represent a sub-group of the first class.
Herschel's immediate object was not classification, and his observations are only recorded in a passing way. But the fact re-
