355 
SCIENTIFIC SUMMARY. 
ASTRONOMY. 
The chances were certainly very much against the present generation wit- 
nessing a repetition of the phenomena so carefully chronicled by Tycho 
Brahe, and which, before his time, had induced Hipparchus to compile his star 
catalogue. Still, since our last Summary was written, a stella nova has 
flashed upon our retinas, and almost as rapidly has disappeared. W e can, 
however, now look down upon Tycho, for he had no spectroscope : the tale 
we have learned by its aid of that strange outburst which took place perhaps 
some hundreds, perhaps some thousands of years ago, is bewildering to a 
degree. We need not here chronicle too many of the attendant circum- 
stances ; suffice it that 2765 of zone +26° in Argelander’s Bonner Stern - 
verzeichniss is a long period variable. Its place for 1855'0 was R.A. 15 h 53 m 
26’9 S and o + 26° 20'E, and its tabulated magnitude 9 ’5. 
On May 16th of the present year this star was observed to be shining like 
a star of the 3rd mag., a brilliancy it lost almost at the rate of a magnitude 
a day for some little time after. Mr. Huggins and several physicists on the 
continent at once attacked the stranger with their spectroscopes with a most 
interesting result, the ordinary stellar spectrum telling of an incandescent 
photosphere and an absorbing atmosphere, was here visible in company with 
another superposed spectrum, consisting of bright lines of various refrangibilities, 
two of the brightest being coincident with those of hydrogen ; so that it seems 
certain that this sudden blaze was in some way connected with those strange 
lines — that is, with incandescent hydrogen and some other substances which 
gave rise to them. 
It is very difficult to imagine conditions which shall bring these agents 
on the scene periodically, but it really seems that this is one of the tasks 
which observers of variable stars must set themselves if they would attempt 
to account for the phenomena in a satisfactory manner. Were our sun a 
trifle more variable than it is, it might, perhaps, help us in this matter ; but 
then possibly there might be drawbacks 1 It is, however, not too much to hope 
that this new fact acquired to physical science will set us working at the whole 
field of variable, new, temporary, and lost stars with renewed interest ; the light 
curves of our variables will be more rigidly scrutinized than ever. From this 
point of view it is interesting to learn that M. Montucci has presented a 
paper to the Paris Academy of Sciences on an arithmetical progression which 
he has observed to result from certain dates contained in the list of temporary 
stars given by Humboldt. The progression starts from 369 A.I)., and the 
difference is 7.75. This gives us the years 369, 393, 827, 1012, 1230, 1578, 
1609, and 1670, in all of which years temporary stars were observed. If the 
hypothesis be correct, these temporary “ stars ’’will be due to eight returns of a 
comet, which must have visited us 193 times between 369 and 1670. 
