Now how are we to interpret these grandiose vicissitudes, visually and spectrally revealed? That we witnessed some great catastrophe is clear. The sudden increase of light of many thousand fold from invisibility to prominence shows that a tremendous cataclysm occurred. The bright lines in the spectrum confirm it and imply that vast upheavals like those that shake the Sun were there in progress, but on so stupendous a scale that, if for no other reason, we must dismiss the idea that explosions alone can possibly be concerned. The dark correlatives of the bright lines have been interpreted as indicating that two bodies were concerned, each travelling at velocities of hundreds of miles a second. But in Nova Aurigæ shiftings of the spectral lines implying six bodies at least were recorded, if such be attributed to motion in the line of sight, and Vogel was minded to throw in a few planets as well—as Miss Clerke pithily puts it. There is not room for so many on the stage of the cosmic drama. Other causes, as we now know, may also displace the spectral lines. Great pressure has been shown to do it, thanks to the labors of Humphreys and Mohler at Baltimore. “Anomalous refraction” may do it, as Professor Julius of Utrecht has found out. Finally, changes of density may produce it, as Michelson has discovered. To these causes we may confidently ascribe most of the shiftings in the stellar spectrum, for just such forces must be there at work. Mr. Monck suggested the idea that new stars are the result of old dark stars rushing through gaseous fields in space and rendered luminous by the encounter. Seeliger revived and developed this idea, which in certain cases is undoubtedly the truth. Probably this occurred to the new star of 1885 which suddenly blazed out almost in the centre of the great nebula in Andromeda. It behaved like a typical nova and in due course faded to indistinguishability. Something like it happened, too, in the nova of 1860, which suddenly flared up in the star cluster 80 Messier, outdoing in lustre the cluster itself, and then, too, faded away. But just as psychology teaches us that not only do we cry because we are sorrowful, but that we are sorrowful because we cry, so while a nova may be made by a nebula, no less may a nebula be made by a star.