The elliptical and irregular classes of nebulæ are illustrated by such splendid examples that we have thought it well to devote a chapter to their separate consideration. One member especially of each towers above the rest, like Ajax among the Argive host, its rival alone excepted, and the two are so different that it is not easy to award the palm of superiority to either. Needless to say that we allude to the objects in Andromeda and Orion, the types respectively of the elliptical and irregular plans of nebular construction.

The former (M 31) is the only real nebula which can readily be detected with the unaided eye, and it is the only one, accordingly, which was discovered in pre-telescopic times. Al Sûfi was familiar with the ‘little cloud’ near the most northern of the three stars in the girdle of Andromeda; and its place was marked on a star-map brought from Holland to Paris by De Thou, and believed to date from the tenth century. Simon Marius, who was the first to turn a telescope upon it, December 15, 1612, called it ‘stellam quandam admirandæ figuræ,’ and compared its dull and pallid rays to those of a candle shining by night through a semi-transparent piece of horn. Yet this strange phenomenon was only rescued from neglect by Boulliaud, whose attention was directed to it by the passage of the comet of 1664 across that part of the sky.