C. HK. Burroy.— Physical Observations of Mars. 153 
October and the end of November. The sun had risen nine degrees higher with 
respect to Mars’ northern hemisphere during this period. But the observed changes 
of the northern snow spot seem to indicate the existence of a variability dependent 
on the position of the Martian First Meridian, and attributable to non-coincidence of 
the centre of the spot with the North Pole of Mars. The drawings have all been 
made by eye estimations of the positions of the spots, without the aid of a micro- 
meter. 
Description of the drawings (Vide Plates VI. and VII.) :— 
No. 1. Longitude of centre of disc=16°7° at 12" 20" G.M.T., on Oct. 25. The 
time given is that at which the original was finished. Observer: J. L. E. Dreyer, 
Esq., who has most kindly forwarded to me a copy of the drawing cited, together 
with his remarks thereon, for embodiment in this paper. The latter were as follows : 
“Mars in 12 in. Equatoreal. Power 300. Definition splendid. Clouds came on at 
11> 57™” (Dunsink mean time). “ Markings near North Pole very easily seen. 
Bright- spot* near limb, south following centre also. Dark line from centre towards 
the north certainly seen.” ‘The preceding remarks are extracted from the Obser- 
vatory note book, those which follow were written on the original drawing. “ Mid- 
way between centre and South Pole is a bright spot, oval p. and f. Canal to north 
very striking.” This drawing affords most valuable support to those drawings made 
at Loughlinstown which represent the same phase or nearly so. 
No. 2. Longitude=26°. 1879, Dec. 1. 10" 26™+010" 54" G.M.T. This drawing, 
like No. 1, includes the marking selected by Beer and Midler as the origin of 
Martian longitudes, passing off towards the western limb. Near to it is shown a 
wedge-shaped space which nearly separates the spot just mentioned (Dawes Forked 
Bay) from that next following it, called by Proctor Beer Bay. Mr. Dreyer in No. 
1 makes this separation complete, prolonging Phillips Island to the east and north 
until it joins Midler Continent. The minute double point of Dawes Forked Bay 
was connected with the dark band surrounding the northern snow region by a 
narrow, slightly curved, dusky stripe. A similar, but oppositely curved dusky line, 
connects the point of Beer Bay with the border of the northern snow spot ; some- 
what as Mr. Dreyer has drawn it. The form here given to the Strait of Herschel 
IJ., and its separation from the neighbouring shadings, impart to it an aspect inter- 
mediate between those under which it is represented by Messrs. Dreyer and Green 
in 1877. Arago Strait and De Cottignez Sea are evident, but between them there 
is a Shaded streak which seems to be new to observation. 
Between the two dusky stripes just mentioned as connected with Dawes Forked 
Bay and Beer Bay, is the place of Knobel Sea, the great dark pear-shaped marking 
* Mr. Dreyer remarks on this, “Iam not quite sure what this bright spot is. Probably it is the 
mouth of the bright streak south of centre.” 
2C2 
