51 A C 
M A C 
M A C 
91 
A T the twelfth letter of our alphabet. As a 
! ^-5 numeral it stands for mille, a thousand ; 
and with a dash over it, thus FT, for a thou- 
[ sand times a thousand, or 1000000. Used as 
| an abbreviature M. signifies Manlius, Marcus, 
Martins, Mucius; and M. Mantus; M. B. 
mulier bona; Mag. Eq. inagister equitum; 
Mag. Mil. magister militum ; M. M. P. ma- 
im mancipio potestate ; M. A. magister ar- 
. tium; MS. manuscript, and M.SS. manu- 
1 scripts, in the plural. In the prescriptions of 
physicians, M. stands for manipulus, a hand- 
ful ; and sometimes for misce, or mixtura. 
MABA, a genus of the triandria order, in 
the dicecia class of plants. The perianthium 
ot the male is trilid ; that of the female is as in 
tlie male ; the fruit is a plum two- celled, su- 
perior. There is one species, a tree of the 
Friendly islands. 
MABEA, a genus of the monoecia poly- 
andria class and order. The calyx is one- 
j leaved; corolla none. There are two species, 
; called pipewood, shrubs of the West Indies. 
MACARONIC, or Macaronian, an ap- 
pellation given to a burlesque kind of poetry, 
made up of a Jumble of words of different 
languages, and words of the vulgar tongue 
! latinized. ' 55 
hi ACE, the second coat or covering of 
the kernel of the nutmeg, is a thin and mem- 
j branaceous substance, of an oleaginous na- 
j tureand a yellowish colour; being met with 
I in flakes of an inch and more in length, which 
j are divided into a multitude of ramifications. 
It is of an extremely fragrant, aromatic, and 
I agreeable flavour, 'and of a pleasant, but 
■ acrid and oleaginous taste. See Myristica. 
MACERATION, in pharmacy, is an in- 
fusion of, or soaking ingredients in, water, or 
j any other fluid,; in order either to soften them 
: or draw out their virtues. 
MAC Id i N E. See Mechanics. 
MACRREL. See Scomber. 
MACROCNEMON, a genus of the class 
I fmd order pentandria monogynia. The cor. 
j is bell-shaped ; the capsule two-celled, two- 
valved; seeds imbricate. There are three 
j species, small trees of the West Indies. 
MAC ROLOBl U M, a genus of the class 
and order triandria monogynia. The calyx 
is double, pet. five, germ, pedicelled legume. 
' There are three species, trees of Guiana. 
MACULiE, in astronomy, are dark spots 
[appearing on the luminous surfaces of the sun 
land moon, and even some of the planets. 
iThe solar maculae are dark spots of an irre- 
I gular and changeable figure, observed in the 
i tale of tlie sun. These yvere first observed 
in November and December of the year 
1610, by Galileo in Italy, and Harriot in Eng- 
land, unknown to, and independant of, each 
other, soon after they had made or procured 
telescopes. 
There have been various observations made 
of the phenomena of the solar macula?, and 
hypotheses invented for explaining them. 
M. 
Many of those macula? appear to consist of he- 
terogeneous parts; the darker and denser 
being called, by Hevelius, nuclei, which are 
encompassed a*s it we A with atmospheres, 
somewhat rarer and less obscure; but the 
figure, both of the nuclei and entire macula?, 
is variable. These macula? are often subject 
, to sudden mutations. In 1644 Hevelius ob- 
served a small thin macula, which in two 
days time grew to ten times its bulk, appear- 
ing also much darker, and having a larger 
nucleus: the nucleus began to fail sensiblv 
before (he spot disappeared; and before it 
quite vanished, it broke into four, which re- 
united again two days after. Some macula- 
have lasted 2, 3, 10, 15,20, 30, but seldom 40 
days; though Kirchius observed one in 1681, 
that was visible from April 26th to the 17th 
of July. It is found that the spots move 
over the sun’s dist with a motion somewhat 
slacker near the edge than in the middle 
parts; that they contract themselves near .the 
limb, and in the. middle appear larger ; that 
they often run into one in the disc, though 
separated near the centre ; that many of them 
first appear in the middle, and many disap- 
pear there; but that none of them* deviate 
lrom their path near the horizon; whereas 
Hevelius, observing Mercury in the sun near 
the horizon, found him too low, being depress- 
ed 27 " beneath his former path. 
From these phenomena are collected the 
following consequefices: 
1. That since Mercury’s depression below 
his path arises from his parallax, the macula?, 
having no parallax from the sun, are much 
nearer him than that planet. 
2. r I hat since they rise and disappear again 
in the middle of the sun’s disc, and undergo 
various alterations with regard both to bulk, 
figure, and density, they must be formed de 
novo, and again dissolved about the sun; and 
hence some have inferred, that they are a 
kind of solar clouds, formed out of his exha- 
lations; and if so, the sun must have an at- 
mosphere. 
3. Since the spots appear to move very 
regularly about the sun, it is hence inferred, 
that it is not that they really move, but that 
the sun revolves round his axis, and the spots 
accompany him, in the space of 27 days, 12 
hours, 20 minutes. 
4. Since the 1 sun appears with a circular 
disc in every situation, his figure, as to sense, 
must be spherical. 
The magnitude of the surface of a spot may 
be estimated by the time of its transit over a 
hair in a fixed telescope. Galileo estimates 
some spots as larger than both Asia and Afri- 
ca put together ; but if he had known more 
exactly the sun’s parallax and distance, as 
they are known now, he would have found 
spme of those spots much larger than the 
whole surface of the earth. For in 1612 he 
observed a spot so large as to be plainly visible 
to the naked eye, and therefore it subtended 
M2 
an angle of about a minute. But the earth) 
seen at the distance of the sun, would sub- 
tend an angle of only about 177' ; therefore 
the diameter of tlie spot was to the diameter 
of the earth, as 60 to 17, or 3$ to 1 nearly ) 
and consequently the surface of the spot," if 
circular, to a great circle of the earth, as 12$ 
to 1, and to the whole surface of the earth) 
as 12J to 4, or nearly 3 to 1. Gassendus 
observed a spot whose breadth was JL. °f the 
sun’s diameter,- and which therefore subtend- 
ed an angle at the eye of above a minute and 
a half, and consequently its surface wasabove 
seven times larger than the surface of the 
whole earth. lie says lie observed above 
40 spots at once, though without sensibly di- 
minishing the light of the sun. 
In the year 1779 there was a spot on the 
sun which was large enough to be seen by the 
naked eye. . It was divided into two parts, 
and must have been 50,000 miles in diameter. 
Various opinions have been formed con- 
cerning the nature, origin, and situation of 
the solar spots ; but the most probable seem* 
to be that of Dr. Wilson, professor of prac- 
tical astronomy in the university of Glasgow. 
By attending particularly to the different 
phases presented by the umbra, or shady 
zone, of a spot of an extraordinary size that, 
appeared on the sun, in the month of No- 
vember 1769, during its progress over the 
solar disc, Dr. Wilson was led to form a 
new and singular conjecture on tlie nature 
of these appearances; which he afterwards 
greatly strengthened by repeated observa- 
tions. The results of these observations are, 
that the solar macula? are cavities in the body 
ofthe sun; that the nucleus, as the middle or 
dark part has usually been called, is the bot- 
tom of the excavations; and that the umbra, 
or shady zone surrounding it, is the shelving 
sides of the cavity. Dr. Wilson, besides 
having satisfactorily ascertained the reality of 
these immense excavations in the body of the 
sun, has also pointed out a method of mea- 
suring the depth of them. fje estimates, in 
particular, that the nucleus dr bottom ofthe 
large spot above-mentioned, was not less than 
a semidiameter of the earth, or about 4000 
miles below the level of the sun’s surface; 
while its othtu - dimensions were of a much 
larger extent. He observed that a spot near 
the middle ©f the sun’s disc is surrounded 
equally on all sides with its umbra ; but that 
when, by its apparent motion over the sun’s 
disc, it comes near the western limb, that 
part of the umbra which is next tlie sun’s 
centre gradually diminishes in breadth, till 
near the edge of the limb it totally disap- 
pears ; whilst the umbra on the other side of 
it is little or nothing altered. After a semi-re- 
volution ofthe sun on his axis, if the spot ap- 
pear again, it will be on the opposite side of 
the disc, or on the left hand, and the part of 
the umbra which had before disappeared is 
now plainly to be seen ; while the umbra ou 
