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change of the terrestrial poles (here on 
earth, of the earth’s diurnal motion) not of 
their pointing to this or that of the fixed 
stars ; for if the poles of the diurnal motion 
remain fixed to the same place on the 
earth, the meridians which pass through 
these poles must be the same. But this 
notion of the changes of the meridian, seems 
overthrown by an observation of M. Clia- 
zelles, of the French academy of sciences, 
who, when in Egypt, found that the four 
sides of a pyramid, built 3000 years ago, 
still looked very exactly to the four cardi- 
nal points ; a position, which could never 
be looked on as fortuitous. 
The mei idian on the globe or sphere, is 
represented by the brazen circle, in which 
the globe hangs and turns. It is divided 
into four times 90, or 360°, beginning at the 
equinoctial. See Globe. On it, each way 
from the equinoctial, on the celestial globes, 
is counted the south and north declination 
of the sun or stars j and on the terrestrial 
globe, the latitude of places north or south. 
There are two points of this circle, which 
are called the poles of the world ; and a dia- 
meter continued from thence through the 
centre of either globe, is called the axis of 
the eai'th or heavens, on which they are sup- 
posed to turn round. On the terrestrial 
globes there are usually thirty-six meridians 
drawn, one through every tenth degree of 
the equator, or through every tenth de- 
gree of longitude. The uses of this circle 
are, 1. To set the globes to any particular 
latitude. 2. To shew the sun’s or a star’s 
declination, right ascension, or greatest al- 
titude, &c. 
“ To find the sun’s meridian altitude or 
depression at night, by the globes.” Bring 
the sun’s place to the meridian above the 
horizon for his altitude at noon ; which will 
shew the degrees of it, counted from the 
horizon. For his midnight depression be- 
low the north-point of the horizon, you 
must bring the opposite point to the sun’s 
present place, as before to the meridian; 
and the degrees there intercepted between 
that point and the horizon, are his midnight 
depression. 
Meridian line is an arch, or part of the 
meridian of a place, terminated each way 
by the horizon. Or it is the intersection 
of the plane of the meridian of the place 
with the plane of the horizon, vulgarly 
called a north and south line, because its 
direction is from one pole towards the 
other. It is of great use in astronomy, 
geography, dialling, &c. and on its exactness 
all depends; whence divers astronomers 
MER 
have taken infinite pains to have it to the 
last precision. 
Mehidian linCy on a dial, is a right line 
arising from the intersection of the meri- 
dian of the place, with the plane of the 
dial ; this is the line of twelve o’clock, and 
from hence the division of the hour-lines 
begin. See Dial. 
Meridian, magnetical, is a great circle 
passing through the magnetical poles, to 
which the magnetic needle, or needle of 
the mariner’s compass, conforms itself. 
Meridian altitude of the sun and stars, 
is their altitude when in the meridian of the 
place where they are observed. Or it may 
be defined, an arch of a great circle per- 
pendicular to the horizon, and comprehend- 
ed between the horizon and the sun or star 
then in the meridian of the place. 
“ To take the meridian altitude with a 
quadrant.” If the position of the meridian 
be known, and the plane of an asti’ono- 
mical quadrant be placed in the meridian 
line, by means of the plumb-line suspend- 
ed at the centre, the meridian altitudes of 
the stars, which are the principal observa- 
tions whereon the whole art of astronomy 
is founded, may easily be determined. The 
meridian altitude of a star may likewise be 
had by means of a pendulum-cloqk, if the 
exact time of the star’s passage over the 
meridian be knowm. Now it must be ob- 
served, that stars have the same altitude 
for a minute before and after their passage 
by their meridian, if they be not in or near 
tlie zenith ; but if tliey be, their altitudes 
must be taken every minute when they are 
near the meridian, and their greatest alti- 
tudes will be the meridian altitudes sought. 
MERIDIONAL distance, in naviga- 
tion, is the same with the departure, east- 
ing or westing, or the difference of longi- 
tude between the meridian under which the 
ship now is, and any other meridian she 
was before under. 
Meridional parts, miles, or minutes, 
in navigation, are the parts by which the 
meridians in Mr. Wright’s chart (com- 
monly though falsely called Mercator’s) do 
increase as the parallels of latitude de- 
crease : and as the cosine of the latitude of 
any place, is equal to the radius or semi- 
diameter of that parallel ; therefore, in the 
true sea-chart, or nautical planisphere, this 
radius being the radius of the equinoctial 
or whole sine of 90°, the meridional parts 
at each degree of latitude must increase, 
as the secants of the arch, contained be- 
tween that latitude and the equinoctial, de- 
crease. The tables, therefore, of meridio- 
