358 Mr. Schroeter’s Observations 
The first appearance of Jupiter’s western limb was very dis- 
tinct at n h 43' 54". 
Emersion of the eastern limb, as distinct, at n h 45' 33", 5. 
N. B. This emersion took place, as represented in fig. 4, to 
the north-eastward of Seneca (B, Tab. VIII. of the Frag.), at 
about the 23d degree of N. lat. 
The emersion of the next, or third satellite, was not ob- 
served. 
That of the fourth was distinct, at 1 i h 59' 1". 
This observation gave me the more satisfaction, as it sin- 
gularly contributed to confirm the discovery I had been so 
fortunate as to make of the twilight in the moon, and the 
height and density of the lower stratum of its atmosphere. 
Experience has sufficiently proved, that a stronger will ever 
obscure a fainter light ; and it follows hence, that the light of a 
bright star approaching the moon, when full, or nearly so, 
will lose something of its lustre: but little can be inferred 
in favour of an atmosphere either of the moon, or of Mars, 
from the observation of Cassini, in which, as Dr. Herschel 
has illustrated by some observations of his own,* a star in 
Aquarius, of the sixth magnitude, and as yet six minutes dis- 
tant from Mars, diminished in light when both were seen in 
the same field of the telescope. A mere apparent diminution of 
light, occasioned by the glare of a larger luminous object, when 
seen at the same time with a smaller one, in the field of the 
telescope, is one thing ; and another thing is a real indistinct- 
ness of the small luminous body, which increases in proportion 
as they approach nearer to each other. 
* Phil. Trans, for the Year 1784, Part II. p. 271, 
