470 The Atmospheres of the Planets. [O&tober, 
Venus, showing the presence of seas, and rendering it pro- 
bable that this planet, like the earth and Mars, must possess 
arctic and antarctic cold ice zones which, reflecting those rays 
refracted obliquely on them, would appear as a white spot. 
To this refraction of the solar rays by the atmosphere of 
Venus may perhaps, in great part, the appearance of 
the planet when near conjunction as a black disc on a 
lighter ground be ascribed; the dark portion of the planet 
being defined partly by light refracted, and partly by light 
reflected, from the planet’s atmosphere. 
A feature of peculiar interest noticed during the late 
transit was a faint grey halo around Venus, perhaps ten 
seconds of arc in breadth, or over one thousand miles, and 
this appears also to be detectable in the photographs. That 
it could possess nothing in common with the bright extremely 
narrow line due to the refraction of the solar rays by the 
atmosphere of Venus its great size leaves unquestionable ; 
for the atmosphere of Venus must be considered absolutely 
evanescent at only one-tenth of the breadth of this halo of 
dull light, whilst its having been photographed shows it is 
not a matter of contrast. It appears to have been only 
visible around the portion of Venus on the sun; but border- 
ing the planet on the solar disc the photographs show an 
extra deposit of silver, probably in some way connected with 
this remarkable halo, though possibly this last may be, as 
suggested by Ranyard, of independent origin, it having been 
found during photographs of solar eclipses. From its small 
breadth the atmospheric fringe of Venus will exert so small 
an influence that there will be no need to take its effe¢ts 
into consideration in determining the solar parallax from 
the results of the late transit, except in considering the 
time of contact obtained by the use of the spectroscope. 
In these observations the effects of the refraction of the 
solar rays by Venus might, perhaps, be found to require 
attention in determining the instant of contact, and indeed, 
from these observations, an independent determination of 
the horizontal refraction might be obtained. 
With regard to Mercury, the slight acquaintance with the 
appearance of this planet renders its probable atmospheric 
condition less certain than in the case of its two companions, 
Venus and Mars. Yet the presence of an atmosphere indi- 
cated by the observation of Schroter, Madler, and Secchi, is 
fully confirmed by the bright, though extremely delicate, 
ring observed round the planet during its solar transits. 
Like Venus, the real surface of the planet appears covered 
with dense masses of cloud usually, and only very rarely 
