SCIENTIFIC SUMMARY. 
419 
~ten or twelve weeks in the time of perihelion passage, would have entirely- 
altered the character of the comet's orbit, whereas the only circumstance 
that enabled astronomers to identify the meteors of November 27, 1872, as 
attendants on Biela’s comet and following in its track, was the observed 
agreement of their motions with those of bodies so travelling. On the 
whole, while it seems to us exceedingly probable that Andromeds or atten- 
dants on Biela’s comet will be seen on the night of November 27, or perhaps 
a day or so earlier or later, we believe there is scarcely any, if any, chance 
whatever, of rediscovering the comet itself. The search ought to be made 
rather (we may now rather say, should have been made) where the comet 
should be seen, if not too completely dissipated, than where the meteoric 
flight, or either of Pogson’s clouds, might be if really following in the track 
of the comet. We trust that small though the chance may be of obtaining 
fresh information respecting this remarkable comet, astronomers will watch 
carefully for the November Andromeds. As Hind says, “there is great 
Justice in M. Otto Struve’s remark: ‘ Kein Comet gebe mehr Ansichtuber die 
Natur der Cometen im Allgemeinen etwas zu erfahren, als der Biela’sche.’ ” 
Sola?' Tai'allax deduced from Observations of Mars. — Mr. Gill gives as the 
result of his observations of Mars, during the opposition of 1877 (it will be 
remembered that Mr. Gill visited Ascension Island to make these observa- 
tions) a solar parallax of 8. "78 ± OZ'015, corresponding with a solar distance 
of about 93,098,000 miles. This distance is considerably greater than that 
which Professor Newcomb regards as the most probable mean (about 
92,400,000 miles) of all the best observations. It agrees well with the 
distance resulting from the combination of Struve’s constant of aberration 
with Cornu’s determination of the velocity of light ; but the constant of 
aberration can hardly be regarded as determined with a degree of accuracy 
sufficient to enable us to determine the real distance as accurately as by 
other methods, even if Cornu’s determination of the velocity of light be con- 
sidered trustworthy, within the necessary limits. On the whole, the result 
of Mr. Gill’s observations will probably be regarded by most astronomers as 
disappointing, simply because it was hoped that it would serve to remove 
doubts as to the sun’s true distance, instead of increasing them. But 
whether this is due to error in other estimates, or to the inferiority of the 
method used by Mr. Gill, is a point on which we should not care to express 
an opinion. 
Tidal Theoi'y of the Evolution of Satellites. — Mr. G. H. Darwin has sug- 
gested a theory of the evolution of satellites which is worth careful con- 
sideration. But it is vitiated so far as his treatment of the matter is 
concerned by an assumption the reverse of the truth. He remarks that 
if a planet were formed of fluid, it would assume a spheroidal shape under 
the influence of the planet’s [rotation, but if a satellite revolves in a circular 
orbit round the planet in the plane of the equator, tides will be raised in the 
planet, such that the spheroid will become distorted into an ellipsoid with 
three unequal axes, and the longer axis of the equator will always be directed 
towards the satellite. Thus the shape of the planet revolves along with the 
satellite, whilst each particle of fluid revolves with the planet, and has therefore 
to rise and fall twice in every revolution of the planet relatively to the satellite. 
Starting from this position, and taking into account the effects of friction, 
e k 2 
