SCIENTIFIC SUMMARY. 
307 
sures of the principal groups of bright lines which present themselies when 
the induction-spark is passed through this gas. The result was to show 
that the bands of Uranus cannot be ascribed to the absorption of this gas. 
There is no absorption band at the position of the line of sodium.’’ 
Further, “ there are no lines in the spectrum of Uranus at the positions of 
the principal groups produced by the absorption of the Earth’s atmosphere.” 
The presence of hydrogen in the atmosphere of Uranus in quantities sufficient 
to produce recognisable absorption (if the coincidence above described be 
confirmed) must be regarded as a fact of singular interest and importance. 
The line is altogether too strong to be regarded as representing merely the 
Fraunhofer F line in the reflected solar light. 
The supposed Change of Colour of the Equatorial Belt of Jupiter. — At the 
May meeting of the Royal Astronomical Society a discussion was raised 
upon this subject, and the general opinion of those who took part in the 
discussion — including Drs. Huggins and De La Rue, the President (Mr. 
Lassell), and others — was that no change had taken place of late in the 
colour of the planet. It was suggested that the colour of the equatorial belt 
is seen now by more observers than in former years, simply because more 
observers use silvered glass reflectors of large aperture. Mr. Browning, 
however, points out that this explanation will not hold good. 11 Five years 
ago,” he says, u I began making careful coloured drawings of Jupiter, with 
a reflector 10^ inches in aperture. As long since as December 13, 1867, I 
drew attention to the fact that colour is best seen with small apertures or 
high powers. I worked with powers of from 350 to 500, when the air 
would permit. Although at that time I easily saw the coppery-grey of the 
dark belts, and the bluish-grey of the poles, I could detect no strong colour 
on the equatorial belt. Yet for the last two years the tawny colour of the 
equatorial belt has been more conspicuous than either. It is true that 
during the last three years I have had a 12^- inch reflector, but, owing to 
unfavourable atmospheric conditions, practically I have seldom indeed used 
more than 10 inches of aperture. Several observers have also seen the 
tawny colour of the belt with both refractors and reflectors of only three or 
four inches’ aperture. The exact colour of the equatorial belt may be 
obtained by allowing a very powerful light to shine through a jet of steam, 
so that an increase in the luminosity of the body of the planet would com- 
pletely account for the colour of the belt.” Adhuc subjudice lis est. 
Proposal for a double Automatic Spectroscope with Compound Prisms . — 
Encouraged by the success with which Mr. Browning has carried out the 
plan devised by Mr. Proctor for a double automatic spectroscope (an instru- 
ment on this plan was exhibited at the last soiree of the Royal Society), 
Mr. Proctor has proposed a double battery with compound prisms, instead 
of the single prisms of the former. The mechanical contrivance differs in no 
essential respect from the former (slightly modified from the picture in The 
Sun), on which the double battery of single prisms was constructed ; but the 
form of the intermediate prism is necessarily modified, since this prism as 
well as the rest has to be compound. The dispersion which would be given 
by this instrument would correspond to that given by thirty-six single 
equilateral prisms of heavy flint glass. 
It is to be noticed that the plan by which the light is made to pass twice 
