rk
transits;[1062] and his observation, repeated August 3, 1891, was
completely verified by Schaeberle and Campbell, who ascertained,
moreover, that the longer axis of the prolate body was directed towards
Jupiter's centre.[1063] The ellipticity of its companions was determined
by Pickering and Douglass; indeed, that of No. 3 had long previously
been noticed by Secchi.[1064] No. 3 also shows equatorial stripes,
perceived in 1891 by Schaeberle and Campbell,[1065] and evident later to
Pickering and Douglass;[1066] nor need we hesitate to admit as authentic
their records of similar, though less conspicuous markings on the other
satellites. A constitution analogous to that of Jupiter himself was thus
unexpectedly suggested; and Vogel's detection of lines--or traces of
lines--in their spectra, agreeing with absorption-rays derived from
their primary, lends support to the conjecture that they possess gaseous
envelopes similar to his.

The system of Jupiter, as it was discovered by Galileo, and investigated
by Laplace, appeared in its outward aspect so symmetrical, and displayed
in its inner mechanism such harmonious dynamical relations, that it
might well have been deemed complete. Nevertheless, a new member has
been added to it. Near midnight on September 9, 1892, Professor Barnard
discerned with the Lick 36-inch "a tiny speck of light," closely
following the planet.[1067] He instantly divined its nature, watched its
hurried disappearance in the adjacent glare, and made sure of the
reality of his discovery on the ensuing night. It was a delicate
business throughout, the Liliputian luminary subsiding into invisibility
before the slightest glint of Jovian light, and tarrying, only for brief
intervals, far enough from the disc to admit of its exclusion by means
of an occulting plate. The new satellite is estimated to be of the
thirteenth stellar magnitude, and, if equally reflective of light with
its next neighbour, Io (satellite No. 1), its diameter must be about one
hundred miles. It revolves at a distance of 112,500 miles from Jupiter's
centre, and of 68,000 from his bulging equatorial surface. Its period of
11h. 57m. 23s. is just two hours longer than Jupiter's period of
rotation, so that Phobos still remains a unique example of a secondary
body revolving faster than its primary rotates. Jupiter's innermost moon
conforms in its motions strictly, indeed inevitably, to the plane of his
equatorial protuberance, following, howe