154 C. E. Burroy.—Physical Observations of Mars. 
shown in the drawings of many observers in the years 1869 to 1873, including 
Messrs. Terby, Knobel (after whom Mr. Green has named this marking), Green, 
and the author of the present notice. The marking in question was apparently 
concealed by snow or some analogous cause dependent on the Martian seasons, 
since it has, so far as I am aware, only been visible during the summer of Mars’ 
northern hemisphere ; although its latitude does not in itself militate against its 
being distinctly visible even during the midsummer of Mars’ southern hemi- 
sphere. 
Instrument: 8 in. reflector, with powers of 270 and 380, chiefly the former. 
Definition at times very good, showing the southern snow as a very narrow zone 
just detached from the limb at the middle of its length. 
No. 8. Longitude=28°. 1879, Oct. 24. 12" 18™ to 12" 49" G.M.T. Almost the 
same aspect as that depicted in No. 2, but considerabie differences in detail 
are evident. Phillips Island does not extend so far eastward as in the two 
previously mentioned drawings, and is not even imperfectly connected with the 
Miidler continent. Christie Bay, with some of the neighbouring markings is, how- 
ever, distinctly visible. A white spot (a) is shown close to the western (W.) limb, 
nearly in the position of Hirst Island, this being the only occasion on which that 
spot appears to have been seen at the last opposition, though it was repeatedly 
detected in 1877. A dusky stripe, not seen in 1877,* runs north-westward from 
Christie Bay. The space about the South Pole is much lighter in this drawing than 
in No. 2, and displays much less detail. The dark markings were visible much 
closer to the eastern than to the western limb of Mars. 
Instrument : 8 in. reflector, powers 220 and 270, the former being a triple achro- 
matic combination giving exquisite definition. 
No. 4. Longitude=36°. 1880, Jan. 5. 8°18" to 9° 0™G.M.T. The dusky stripes 
running northward from Dawes Forked Bay, and from Beer Bay were very distinct. 
A portion of another streak, of similar appearance, and directed from the neigh- 
bourhood of the North Pole towards Christie Bay, was seen. The two points of 
Dawes Forked Bay appeared as one, melting into the streak connected with them, 
while Beer Bay seemed to terminate in a defined point of darker shade than the 
stripe proceeding from it. A number of other minute details were seen by glimpses, 
too transient to permit their true form and disposition to be satisfactorily seized. 
They consisted chiefly of irregularities in the northern boundary of De La Rue 
Ocean following Beer Bay. The revelation of these was probably due to the 
increased aperture made use of on this occasion, namely, twelve inches of silvered 
glass, and a magnifying power of 408 diameters. Dawes’ Forked Bay and Beer 
Bay are nearly separated by a kind of veil which almost reaches the east end of 
Phillips Isiand. 
* Except by Schiaparelli. See summary, page 170. 
