On the 24th, however, so soon as it began to wane, the bright lines of hydrogen were conspicuous with their dark correlatives, just as they had been with Nova Aurigæ and other novæ. At the same time each particular spectral line proved a law unto itself, some shifted more than others, thus negativing motion as

their only cause and indicating change of pressure or density as concerned concomitants of the affair. Blue emissions like those of Wolf-Rayet stars next made their appearance; then a band, found by Wright at the Lick to characterize nebulæ, shone out, and finally in July the change to a nebular spectrum stood complete.

Then came what is the most suggestive feature in the whole event. On August 22 and 23 Dr. Wolf at