MER 
minary. Very frequently, he goes so near 
the sun as to be 'lost altogether in his rays. 
When he begins to make his appearance in 
the evening after sunset, he can scarcely at 
first be distinguished in the rays of the twi- 
light. But the planet disengages itself more 
and more, and is seen at a greater distance 
from the sun every successive evening ; and 
having got to the distance of about 22° 5' , 
it begins to return again. During this in- 
terval, the motion of Mercury^ referred to 
the stars, is direct ; but when it approaches 
within 18° of the sun, it appears for some 
time stationary ; and then its motion begins 
to be retrograde. The planet continues to 
approach the sun, and at last plunges into 
his rays in the evening, and disappears. 
Soon after, it may be perceived in the 
morning, before sunrise, separating further 
and further from the sun, his motion being 
retrograde, as before he disappeared. At 
the distance of 18° it becomes stationary, 
and assumes a direct motion, continuing, 
however, to separate, till it comes to 22°.S 
of distance ; then it returns again to the 
sun, plunges into his rays, and appears soon 
after in the evenine, after sunset, to repeat 
the same career. The angular distance fi-om 
the sun, which the planet reaches on both 
sides of that luminary, varies from 16° to 
nearly 28°. The duration of a co'mplete os- 
cillation, or the interval of time that elapses 
before the planet returns again to the point 
from which it set out, varies also from 100 
to 130 days. The mean arc of his retro- 
gradation is about 131 o ; its mean duration 
twenty-three days ; but the quantity differs 
greatly in different retrogradations. In ge- 
neral, the laws of the movements of Mer- 
cury are verj’ complicated ; he does not 
move exactly in the plane of the ecliptic ; 
sometimes he deviates from it more than 6°. 
Some considerable time must have elapsed 
before astronomers suspected that the stars 
which were seen approaching the sun in the 
evening and in the morning were one and 
the same. The circumstance, however, of 
the one never being seen at the same time 
with the other, would gradually lead them 
to the right conclusion. The apparent dia- 
meter of Mercury varies as well as that of 
the sun and moon, and this variation is ob- 
viously connected with his position rela- 
tively to the sun, and with the direction of 
his movement. The diameter is at its mi- 
nimum when the planet plunges into the so- 
lar rays in the morning, or when it disen- 
gages itself from them ; it is at its maxi- 
mum when the planet plunges into the solar 
MER 
rays in the evening, or when it disengages 
itself from them in the evening ; that is to 
say, when the planet passes the smi in its 
retrograde motion, its diameter is the great- 
est possible ; when it passes the sun in its 
direct motion, it is the smallest possible ; 
and the mean length of the apparent dia- 
meter of Mercury is 11". Sometimes, 
when the planet disappears during its retro- 
grade motion, that is to say, when it 
plunges into the sun’s rays in the evening, 
it may be seen crossing the sun under the 
form of a black spot, which describes a 
chord along the disk of the sun. This black 
spot is recognized to be the planet, by its 
position, its apparent diameter, and its re- 
trograde motion. These transits of Mer- 
cury, as they are termed, are real annular 
eclipses of the sun : they demonstrate that 
the planet is an opaque body, and that it 
borrows its light from the sun. When exa- 
mined by means of telescopes, magnifying 
about 200 or 300 times, he appears equally 
luminous throughout his whole surface, 
without the least dark spot. But he exhi- 
bits the same difference of phases with the 
moon, being sometimes horned, sometimes 
gibbous, and sometimes shining almost with 
a round face, though not entirely full, be- 
cause his enlightened side is never turned 
directly towards us ; but at all times per- 
fectly well defined without any ragged 
edge, and perfectly bright. Like the moon, 
the crescent is always turned towards the 
sun. These different phases throw consi- 
derable light on the orbit of Mercury. See 
Venus. 
Mercury, in heraldry, a term used, in 
blazoning by planets, for the purple co- 
lour in the arms of sovereign princes. See 
Blazoning. 
MERGER, in law, is where a less estate in 
lands, &c. is drowned in the greater ; as if 
the fee come to the tenant for years or life, 
the particular estates are merged in the 
fee ; but an estate tail cannot be merged in 
an estate in fee ; for no estate in tail can be 
extinct by the accession of a greater estate 
to it. 
MERGE S, in natural history, the Mergan- 
ser, a genus of birds of the order Anseres. 
Generic character: bill serrated, slender, 
and hooked at the point; nostrils small, 
oval, and near the middle of the bill ; feet - 
four-toed, the outer one before longer than 
the middle one. There are ten species, of 
which we shall notice the following. M. 
merganser, the goosander, weighs about 
four pounds, and is twenty-eight inches 
