always in progress above sun-spots; but the long duration of the star's
suddenly acquired lustre did not easily fit in with the adopted
rationale. A direct collision, on the other hand, was out of the
question, since there had obviously been little, if any, sacrifice of
motion; and the substitution of a nebula for one of the "stars"[1487]
compelled recourse to scarcely conceivable modes of action for an
explanation of the perplexing peculiarities of the compound spectrum.

PLATE V.

[Illustration: Photographic and Visual Spectrum of Nova Aurigae.

Fig. 1.--From a Photograph taken by Sir William and Lady Huggins, Feb.
22, 1892.

Fig. 2.--From a Drawing made by Lady Huggins, Feb. 2 to 6, 1892.]

An unexpected _denouement_, however, threw all speculations off the
track. The Nova contained most of its brightness, fluctuations
notwithstanding, until March 9; after which date it ran swiftly and
uniformly down towards what was apprehended to be total extinction. No
marked change of spectrum attended its decline. When last examined at
Tulse Hill, March 24, all the more essential features of its prismatic
light were still faintly recognisable.[1488] The object was steadily
sinking on April 26, when a (supposed) final glimpse of it was caught
with the Lick 36-inch.[1489] It was then of about the sixteenth
magnitude. But on August 17 it had sprung up to the tenth, as Professors
Holden, Schaeberle, and Campbell perceived with amazement on turning the
same instrument upon its place. And to Professor Barnard it appeared,
two nights later, not only revived, but transformed into the nucleus of
a planetary nebula, 3" across.[1490] The reality of this seeming
distension, however, at once disputed, was eventually disproved. It
unquestionably arose from the imperfect focussing power of the telescope
for rays of unusual quality.[1491]

The rekindled Nova was detected in this country by Mr. H. Corder, on
whose notification Mr. Espin, on August 21, examined its nearly
monochromatic spectrum.[1492] The metamorphosis of Nova Cygni seemed
repeated.[1493] The light of the new object, like that of its
predecessor, was mainly concentrated in a vivid green band, identified
with the chief nebular line by Copeland,[1494] Von Gothard,[1495] and
Campbell.[1496] The second nebular line was also represented. Indeed,
the last-named observer recognised nearly all the eighteen lines
measured by him in the Nova as characteristic of planetary nebulae