indigenous to the stars, for it seemed not at all impossible that there might be some optical explanation of colours so vividly contrasted emanating from points so contiguous. It was also remembered that blue stars were generally only present as one member of an associated pair, and it was thought, not it must be confessed without plausibility, that the blue hue which was exhibited might have arisen from some subjective cause, or at all events that it did not necessarily imply that the star actually possessed a bluish colour. When, Sir William Huggins showed that the actual spectrum of the object demonstrated that the cause of the colour in each star arose from absorption by its peculiar atmosphere, it became impossible to doubt the reality of the phenomena. Since then it has been for physicists to explain why two closely neighbouring stars should differ so widely in their atmospheric constituents, for it can be no longer contended that their beautiful hues arise from an optical illusion.
Another achievement in the early part of Sir William Huggins' career is connected with the celebrated new star that burst forth in the Crown in 1866. It seemed a fortunate coincidence that just at the moment when the spectroscope was beginning to be applied to the sidereal heavens, a star of such marvellous character should have presented itself. I well remember going with Lord Rosse in 1856 to pay my first visit to Sir William Huggins in Tulse Hill. One of the objects he showed us was the spectrum of this star, which on the 12th of May in that year suddenly burst forth with a lustre of the second magnitude in the constellation of the Northern Crown. At the time of my visit the star had considerably declined from its original radiance. The feature which made the
