SIR JAMES SOUTH ON THE EXTENSIVE ATMOSPHERE OF MARS. 419 
affected by the approach of Mars, than what the brightness of its superior light 
might account for.” — Vide Phil. Trans, vol. Ixxiv. p. 2/2. 
On the 19th of February 1822, in Blackman-street, a star of the 9th or 10th 
magnitude was for several hours seen in the field of the 5-feet Equatorial 
with the planet Mars. At a distance of one minute and forty-three seconds of 
a degree from the planet, (which took place at 1 l b 15 m sidereal time,) its splen- 
dour suffered no sensible diminution. 
On the following night a star 42 Leonis, of the 6th magnitude, was in the 
field of the same instrument with Mars, and the planet’s progress towards the 
star was observed micrometrically for several hours ; nor did the star suffer 
any loss of its brilliancy as its distance from the planet diminished. 
Fatigued by previous watchings, at about two in the morning I retired to 
rest ; but thinking it probable that the star would undergo occupation, accom- 
panied by my brother Mr. Henry South I returned to the instrument about 
4 o’clock, and found Mars about half his own diameter from the star. The 
planet had about twenty-four degrees of altitude ; its limb was at times well 
defined and steady, at other times extremely unsteady ; the star was compara- 
tively steady*, could be kept tolerably well upon the micrometer-wire, and was 
of a beautiful blue colour. At 15 h 3 m 23 s .3 sidereal time, it was seen admirably 
defined, and was distant from the limb of the planet a diameter of one of the 
micrometer-wires, equal nearly to one second of a degree ; from which time 
till 15 h 3 m 53 s the planet’s limb was so extremely unsteady and ill defined, 
that the precise moment of occupation could not be obtained. 
After emersion, at 15 h 20 m 38 s .3 the star was seen when it was about 
diameter of the wire, or one second and a half from the limb ; it was almost 
indigo blue ; and the contrast between it and the planet, which was of a deep 
red, was exquisitely beautiful. By reference to the double star 48 / Cancri, 
some idea of it may be entertained, if we regard the larger of its stars as 
Mars, and the smaller as 42 Leonis. At the time of observation the planet 
had passed his opposition only forty-seven hours, and his apparent diameter 
as measured with the micrometer, was sixteen seconds and six tenths. 
* This steadiness of one sidereal object, as contrasted with the extreme unsteadiness of another, 
seen under similar circumstances of atmosphere and altitude, has long been familiar to me, and is a 
phenomenon to which, on some future occasion, I shall probably invite the Society’s attention. 
