een violently assailed,
the discovery of _Juno_, in 1804, the third one of the group, led to a
careful experimental study of the defining power of the telescope used,
and of the laws governing the phenomena of spurious disks.

With a telescope of about nine inches in aperture, HERSCHEL found that
if _Juno_ subtended an angle greater than a quarter of a second of arc,
a certain indication of the fact would have shown itself in the course
of the experiments. This conclusion was a justification of the name
Asteroid, since the appearance of the new planet was strictly stellar.
On other grounds, a better name might have been selected.

In the paper giving the results of the experiments, the phenomena of the
spurious disks are very completely described; but they did not attract
the attention which they deserved, and they only became an object of
especial interest to students of physics when they were again studied by
the famous German optician FRAUNHOFER, a generation later.

Incidentally the experiments are of interest, as yielding us a measure
of the excellence of HERSCHEL'S telescopes, and a measure which is quite
independent of the keenness of his vision. From them we may be sure that
the efficiency of the nine-inch mirror used was not sensibly less than
that of the highest theoretically attainable excellence. In this
connection, too, we may refer to the _Philosophical Transactions_ for
1790, pp. 468 and 475, where HERSCHEL gives observations of both
_Enceladus_ and _Mimas_ seen in contact with the ball of _Saturn_.
I have never seen so good definition, telescopic and atmospheric, as he
must have had on these occasions.

_Researches on the Spectra of the Fixed Stars._

The spectroscope was applied by SECCHI to the study of the spectra of
the fixed stars visible to the naked eye in the years 1863 to 1866.
He examined the nature of the spectrum of each of the larger stars,
and found that these stars could be arranged in three general classes or
_types_. His results have been verified and extended by other
astronomers, and his classification has been generally accepted.
According to SECCHI, the lucid stars may be separated into three groups,
distinguished by marked differences in their spectra. SECCHI'S Type I.
contains stars whose spectra are like those of _Sirius_, _Procyon_, and
_[alpha] Lyrae_; his Type II. stars like _Arcturus_ and _Aldebaran_;
his Type III. stars like _[alpha] Orionis_.

HERSCHEL