and thus concluded that the evidence was in favour of a red colour in former times. Shortly afterwards, Schiaparelli examined the evidence with equal care and thoroughness and reached an opposite conclusion, showing that the terms used by the ancient authors which might have indicated redness of colour were susceptible of other interpretations; they might mean fiery, blazing, etc., as well as red in colour, and were therefore probably suggested by the extraordinary brightness of Sirius and the strangeness with which it twinkled when near the horizon. In this position a star not only twinkles, but changes its colour rapidly. This change is not sensible in the case of a faint star, but if one watches Sirius when on the horizon, it will be seen that it not only changes in appearance, but seems to blaze forth in different colours.

It seems to the writer that this conclusion of Schiaparelli is the more likely of the two. From what we know of the constitution of the stars, a change in the colour of one of these bodies in so short a period of time as that embraced by history is so improbable as to require much stronger proofs than any that can be adduced from ancient writers. In addition to the possible vagueness or errors of the original writers, we have to bear in mind the possible mistakes or misinterpretations of the copyists who reproduced the manuscripts.

CHAPTER VIII

NEW STARS

It may be glorious to write

Thoughts that shall glad the two or three

High souls, like those far stars that come in sight

Once in a century.-LOWELL

HE stars considered in the preceding chapter go

THE

through their changes of light in a limited and generally more or less regular period, so that a prediction of their brightness at future epochs is in most cases possible. They are distinguished by the remarkable fact, pointed out at the beginning of the chapter, that the period seems to be limited, none so long as two years being yet known.

New stars, or "Nova" as they are frequently called, are distinguished from the irregularly variable stars already described by their blazing forth, so far as is yet known, only once in the period of their his tory.

The limitation of the period seems to form a wellmarked distinction between periodic stars and the irregularly variable ones now to be considered, and to indicate some radical difference in the cause of

variability.

The most remarkable among these stars is undoubtedly Eta Argus, which, though now invisible to the naked eye, was, at various times between 1830 and 1850, of the first magnitude. It falls so closely on a line between the new or temporary stars and those which are irregularly variable that it may form a distinct class. Being in 58° of south declination it is not visible except in latitudes south of 32°. For this reason it could not be made a subject of observation in northern European countries. Of the greatest interest is the question whether it was visible in early historic times. On this question no decisive evidence can be gathered. The catalogues of Ptolemy and Ulugh Beigh are among the earlier authorities which we consult on the subject. Much confusion, however, is found in the data to be consulted. In Halma's edition of Ptolemy's catalogue, two stars in the constellation Argo are marked as having the Bayer letter Eta. But neither of these is near the position of the star under consideration. In fact, Ptolemy's constellation Argo seems scarcely to extend as far east as the point in question. The same remark applies to the medieval catalogue of Ulugh Beigh. The only conclusion we can draw on the subject is that the star was probably not so conspicuous in early historic times as to excite the attention of observers.

On Bayer's charts, published about 1600, there is a star marked Eta, but this is nowhere near the place of the modern Eta, nor is there any star shown in the position of the latter. The fact appears to be that

Bayer's maps of this constellation are so erroneous that little correspondence can be found between his figures and the heavens, and the certain identification of any particular star scarcely seems possible, except in the case of Canopus and possibly a few other bright ones. Near the position of the modern Eta are several small stars marked d, but from what has been said we have no reason to identify these with the star in question.

The first authentic observation of the star is found in Halley's catalogue, made at St. Helena in 1677, where it appears as of the fourth magnitude. The next observation is by Lacaille, who observed it at the Cape of Good Hope about 1750. In the catalogue at the end of his Calum Australe Stelliferum, the star is given as of the second magnitude; but in the original observations it is marked of magnitude 2.3. It may be added that Lacaille was the first one to assign the symbol Eta. From a remark at the end of the catalogue, it seems that he assigned these symbols in accordance with Bayer only when the Bayer stars could be identified, but it would seem that there could have been few such identifications in Argo. In catalogues made between the years 1822 and 1832 it still appears as of the second magnitude; whether this magnitude was an independent one or merely taken from Lacaille may be an open question, but we cannot suppose that the variation from Lacaille's estimate was at all striking. A traveller named Birchell noted it as of the first magnitude in 1827, but this seems doubtful in view of the records of other observers.

Our next authority on the subject is Sir John Herschel, who, during his residence at the Cape of Good Hope, in 1834, noted Eta Argus as of magnitude between first and second. It remained without exciting any suspicion of change to near the end of 1837. In December of this year Herschel's astonishment was excited by the appearance of “a new candidate for distinction among the very bright stars of the first magnitude, in a part of the heavens with which being perfectly familiar, I was certain that no such brilliant object had before been seen.” This was

soon found to be identical with Eta Argus, of which the light had nearly trebled. It decidedly surpassed Procyon, Alpha Orionis, and even Rigel, which was nearest to it. It continued to increase until the beginning of January, 1838, when it was equal to Alpha Centauri. Then it began slowly to fade, but on April 14th, which seems to have been the date of Herschel's last observation, it was still about equal to Aldebaran, and therefore of the first magnitude. It seems to have blazed up again, according to the testimony of observers, in 1843, when it was fully as bright as Canopus, and could not therefore have been far below Sirius. It fluctuated during the following ten years, and then began to fade away slowly. In 1868 it was estimated by Mr. Tebbut as only of the sixth magnitude, and gradually disappeared from vision by the naked eye in the year following. During the last fifteen or twenty years it has generally been of the seventh magnitude, or fainter, and there is no evidence of any approaching renewal of its bright stage of half a