126 L. Trouvelot—Transit of Mercury. 
From the time of first contact till one o’clock in the after- 
of the inter-mercurial planets, or of the luminous ring were 
seen. However, I had a persistant impression of a faint nebu- 
lous cloud on or near the center of the black disc, but notwith- 
standing my efforts, I was not able to satisfy myself whether it 
was real or illusory. 
At about three o’clock the sky cleared up, the definition was 
good; small facule and the granulations being well seen on 
the sun, Mercury was observed with much attention. At this 
time the planet appeared of an intense bluish-black color, much 
darker than in the morning. With the powers 250 and 450, 
the planet lost entirely the flat appearance of a disc, and its 
globular form became very conspicuous and striking ; although 
no difference in the uniformity of its intense bluish-black tint 
was noticeable which could produce this phenemenon. The 
blackness of the disc appeared much more intense than the 
umbra or nucleus of any solar spot I have ever observed, and I 
do not think that any observer familiar with the appearance of 
sun spots, could fora moment be mistaken and take a round 
black spot for a planet in transit, so striking is the difference in 
character. 
The small nebulous cloud observed in the morning on Mer- 
cury still appeared to be there in the afternoon, but while the 
vision had greatly improved by the clear sky, it seemed just as 
faint, ill defined and ghost-like as when the sky was vaporous. 
Great efforts were made to see a definite luminous point in this 
cloud, but nothing of the sort was visible. I was not able to con- 
vince myself of the reality of the phenomenon, and I am rather 
inclined to think it illusory from the well ascertained fact 
that the nebulous cloud was best seen in the afternoon when 
the image was slightly tremulous; but the moment it became 
steady, the phantom cloud vanished entirely, and the dise of 
Mercury appeared of a uniform intense bluish-black color. 
During the whole time of transit, attention was given to the 
supposed inter mercurial planets which might have been in 
transit on the sun with Mercury, but no trace of such bodies 
could be detected, either by direct vision in the telescope or by 
projection on ascreen. If such bodies do really exist and one 
or several were in transit with Mercury, their apparent diame- 
ter must be very small, and at least less than one-half of that 
of the smallest solar granules, asa black object of this size 
could have been easily detected during the afternoon. , 
Although pretty well defined, the edge of the black dise of 
Mercury never appeared very sharp, even during the moments 
of best definition ; nor did its outline appear perfectly smooth, 
