SCIENTIFIC SUMMARY. 
31 1 
Mr. Abbe’s materials might lead to somewhat different results. The subject 
is one which, in the present stage of astronomical progress, deserves to be 
most carefully studied. 
W e do not hear that any views have been obtained of Mars during the 
recent opposition which add much to our knowledge of the features of this 
planet. At a late meeting of the Astronomical Society, Mr. Browning 
exhibited a series of .views which he had obtained with Mr. Barnes’ 8§-inch 
silvered glass reflector. Nearly thirty sketches were made. These agree 
well with those made by Mr. Be la Hue with his 13-inch metal speculum, 
and fairly with the exquisite drawings b} r Mr. Dawes. We have seen 
series of views, by the way, equalling the last named in fullness of detail, 
and in consistency. 
Mr. Huggins has renewed his observations on the spectrum of Mars. 
Using a direct vision spectroscope, he found lines in the spectrum which he 
was enabled to assign to the atmosphere of Mars ; since, while resembling 
lines produced by our own atmosphere in the solar spectrum when the sun 
is low — the situation of Mars precluded the possibility of their being ascribed 
to the earth’s atmosphere. He ascribes the colour of Mars to the nature of 
the soil — a view confirmed by the definite outlines of regions tinted with 
the peculiar ochreish colour characterising Mars, and by the circumstance 
that the polar regions appear white, though they are seen through a greater 
depth of atmosphere than the equatorial regions. The views of Dr. Zollner, 
quoted with favour by Mr. Huggins, do not appear quite so well worthy of 
confidence as those resulting from Mr. Huggins’ own observations. The 
opinion, for instance, that the increased light near the edge of the disc is 
due to the existence of hills having a slope of 76° (as great as that of the 
Peter Botte Mountain) and distributed all over the surface of Mars, appears 
to us bizarre in the extreme. 
Mr. Dawes appends to a valuable paper on the micrometrical measurement 
of double stars, a series of observations most instructive and interesting to 
the telescopist. Our space will not permit us to enter at length into the 
discussion of these, but some results are too remarkable to be passed over 
without comment. The effects produced by changing the figure of a tele- 
scope’s aperture have been carefully studied by Mr. Dawes. A round disc 
placed centrally before the aperture increases the separating power of a 
telescope, but increases both the number and the brightness of the rings 
round the brighter stars. Thus the smaller components of a brighter star 
may be hidden by one or other of the rings. And in this connection another 
observation of Mr. Dawes is noteworthy ; viz. that a larger aperture may 
fail (in appearance) to separate stars clearly divided by a smaller aperture, 
owing to the circumstance, that within the larger instrument, one of the 
rings of light round a star may happen to pass directly through the com- 
panion. A perforated whole aperture may frequently be employed with 
advantage. It has the effect of considerably diminishing the star discs 
owing to the loss of brilliancy, while the full effect of the whole aperture in 
reducing the diameter of the disc is also preserved. A triangular aperture, 
produces an hexagonal star-disc, with bright rays from each side ; these 
rays have an inconvenient effect, sometimes obliterating or distorting a 
small companion. A hexagonal aperture has the power of effectually cor- 
