SIR JAMES SOUTH ON THE EXTENSIVE ATMOSPHERE OF MARS. 421 
ably fine, and although Mars had not more than seven or eight degrees of 
altitude, a power of 320 was used with advantage. 
The diameter of Mars, as taken with the 5-feet Equatorial, was about ten 
seconds. The observations were commenced at about seven hours sidereal 
time, whilst the nearest appulse was perhaps at about eleven hours ; they were 
not made for determining the place of Mars, but for noticing any phenomena 
which the star might exhibit. 
The facts being now before us, the inferences may be comprised in a few 
lines. 
Sir W. Herschel’s observation of the 27th of October 1783, and mine of 
the small star on the 19th of February 1822, are at variance with Cassini’s 
observation, but impugn not the accuracy of Roemer’s ; whilst my observa- 
tions of 42 Leonis and of 37 Tauri, being apparently subversive of the obser- 
vations both of Cassini and of Roemer, point out the “ extensive atmosphere 
of Mars” as a subject meriting further investigation. 
Such are all the observations relative to the extensive atmosphere of Mars 
which my observatory can furnish. One of these, viz. that of the 17th of last 
March, demands further consideration, lest, having served to invalidate one 
hypothesis, it might be brought forward to support another ; namely, that 
“ the red colour of the planet Mars is dependent upon the physical properties 
of his atmosphere.”* Moreover, it seems inconsistent with a previous ob- 
servation. 
The star 37 Tauri had “ nearly the colour of Mars” whilst in contact with 
the planet ; whereas, the star 42 Leonis was “ beautifully blue” previously and 
subsequently to occultation by the planet. The facts are different ; — are they 
reconcileable ? The following then are extracts from the Observatory Journal. 
On the night following the observation of 37 Tauri, namely, the 18th of 
March, “ the five-feet Equatorial was placed upon Mars, in order to compare 
its colour with that of 37 Tauri ; the star and planet were still in the field to- 
gether, though nearly at opposite points of its circumference. “ I can have no 
hesitation in saying, that the star is red, but not of so deep a tint as the planet.” 
“ Mars being placed out of the field, I requested an attendant (accustomed 
to use a telescope) to look at the star and to tell me its colour ; entirely un- 
* Vide Brewster’s Encyclopaedia, vol. ii. pages 636 & 63 7 (article Mars). 
