230 
MOT 
M O U 
M O IT 
right line AB, the distances AC and BC, 
from the common centre of gravity C, are re- 
ciprocally as the weights of the bodies A and 
B, that is, AC I BC : B : A. 
It a line is drawn from the centre of gra- 
vity of a body, perpendicular to the horizon, 
it is called the line of direction; because it is 
the line that the centre of gravity would de- 
scribe if the body fell freely. 
It is the property of this line, that while it 
falls within the base upon which the body 
stands, the body cannot fall; but if it fall 
without the base, the body will tumble. Thus 
the inclining body A BCD, (tig. 166) whose 
centre of gravity is E, stands firmly on its 
base CDiK, because the line of direction EF 
falls within the base. But if a weight, as 
ABGIi, is laid upon the top of the body, 
the centre of gravity of the whole body and 
weight together is raised to L ; and then, as 
the line of direction LD falls without the 
base at I), the centre of gravity is not Sup- 
ported, and the whole body and weight will 
tumble down together. 
Hence appears the absurdity of people’s 
rising hastily in a coach or boat, when it is 
likely to overset-; for by that means they raise 
the centre of gravity so far as to endanger 
throwing It quite out of the base, and if they 
do, they overset the vehicle effectually. 
Whereas, had they clapped down to the bot- 
tom, they would have brought the line of di- 
rection, and consequently the centre of gra- 
vity, farther within the base, and by that 
means might have saved themselves. 
The broader the base, and the nearer 
the line of direction is to the middle or centre 
of it, the more firmly does the body stand. 
On the contrary, the narrower the base, and 
the nearer the line of direction is to the side 
of it, the more easily may the body be over- 
thrown, a less change of position being suffi- 
cient to remove the line of direction out of 
the base in the latter case than in the former. 
And hence it is, that a sphere is so easily 
rolled upon a horizontal plane ; and that it is 
so difficult, if not impossible, to make things 
which are sharp pointed to stand upright on 
the point 
From what has been said, it plainly appears, 
that if a plane CD on which a heavy bodv 
is placed, was elevated at C, the body would 
slide down upon the plane, whilst the line 
of direction falls within the base; but it would 
tumble or roll down when that line falls 
without the base. Thus the body E (tig. 
167) would only slide down, whilst the body 
B would roll down upon it. 
When the line of direction falls within the 
base of our feet, we stand, and most firmly 
when it is in the middle; but when it is out 
of that base, we immediately fall. And it is 
UQt only pleasing, but even surprising, to re- 
flect upon the various methods and postures 
which we use, to retain this position, or to re- 
cover it when lost, without our being sensible 
of it. Tiius we bend our bodies when we rise 
from a chair, or when we go up stairs; and for 
thfs purpose a man leans forward when he 
carries a burden upon his back, and backward 
when he carries it on his breast, and to the 
right or left side as he carries it on the op- 
posite side. 
If a body is suspended freely from different 
centres, its centre of gravity will be in the in- 
tersection formed by lines drawn from those 
.eeatres perpeudicular to the horizon. Hence 
we obtain an easy practical method of finding 
the centre of gravity of any irregular plane 
ligure. Suspend it by any point, with the 
plane perpendicular to the horizon, and from 
the point of suspension hang a plumb line, 
and draw a line upon the body where the 
string passes over ; do the same tor any other 
point of suspension, and where the two lines 
meet must be the centre of gravity ; for the 
centre of gravity being in each line, it must 
be at the point where they intersect. 
Motion, spontaneous or muscular, is that 
performed by the muscles at the command 
of the will. 
Motion, natural or involuntary, that ef- 
fected, without any such command, by the 
mere mechanism of the parts, such as the 
motion of the heart, pulse, &e. 
Motion, intestine, the agitation of the 
particles of which a body consists. 
Motion, in music, the manner of beating 
the measure, to hasten or slacken the time of 
the words or notes. 
MOVEMENT, in mechanics, a machine 
that is moved by clockwork. See Clock- 
work. 
MOULDINGS. See Architecture. 
MOUNTAINS. Elevations consisting 
chiefly- of ejay, sand, or gravel, are called 
hills. Those which consist chiefly of stone 
are called mountains. Mountains are divided 
into primaeval, that is, of equal date with the 
formation of the globe, and secondary or 
alluvial. Among primaeval, those of granite 
hold the first place. The highest mountains 
and most extensives ridges throughout the 
globe are of that kind ; as the Alps and Pyre- 
nees in Europe; the Altuischan, Ural ian, 'and 
Caucasus, in Asia ; and the Andes, in Ame- 
rica. The highest of them never contain 
metallic ores ; but some of the lower contain 
ores of copper and tin. The granite next the 
ore always abounds in mica. Petrifactions 
are never found in these primaeval moun- 
tains. 
That the formation of these mountains pre- 
ceded that of vegetables and animals, is 
justly inferred from their containing no or- 
ganic remains, either in the form of petrefac- 
tion or impression. Naturalists arc agreed, 
that granites were formed by crystallization. 
This operation probably took place after the 
formation of the atmosphere, and the gradual 
excavation of the bed of the ocean, when the 
dry land appeared. For, by means of the 
separation of the aeriform fluids which con- 
stitute the atmosphere, the evaporation of 
part of the water into the atmosphere, and the 
gradual retreat of the remainder, the various 
species of earths, before dissolved or diffused 
through this mighty mass, were disposed to 
coalesce; and among these the siliceous must 
have been the first, as it is the least soluble ; 
but as the siliceous earth has an affinity -to 
the other earths with which it was mixed, 
some of these must have united in various 
proportions, and thus have formed, in dis- 
tinct masses, the feldtspar, schorl, and mica, 
which compose the granite. Calcareous earth 
enters very sparingly into the composition of 
this stone ; but as it is found in schorl, which 
is frequently a component part of granite, it 
follows that it must be one of the primitive 
earths, and not entirely derived from marine 
exuvia', as some have supposed. Quartz can 
never be supposed to be a product of fire ; for 
in a very low heat it bursts, cracks, and loses 
its transparency, and in the highest degree of 
heat that we can produce, is infusible, so that 
in every essential point it is different from 
glass, to which some have compared it. As 
granite contains earths of every genus, we 
may conclude, that all the simple earths are 
original. This, however, is no proof that 
they are in reality simple and uncompounded 
of other principles ; but they must be consi- 
dered as such in the present state of our 
knowledge. r l hough water undoubtedly 
dates from creation, yet late experiments 
have shewn it to be a compound, as was for- 
merly stated. 
Mountains which consist of limestone or 
marbles of a granular or scaly texture, and 
not disposed in strata, seem also to have pre- 
ceded the creation of animals, for no organic 
traces are found in them. Some of those 
which consist of argillaceous stones, and some 
of the siliceous, contain also no organic re- 
mains. These olten consist of parallel strata 
of unequal thickness ; and the lower are harder 
and less thick than the upper, and therefore 
seem to have been formed earlier than the 
upper. 
Alluvial mountains are evidently of poste- 
rior formation, as they contain petrifactions 
and other vestiges of organic substances, and 
these are always stratified. 
Mountains, as to structure, are entire, stra- 
tified, and confused. Entire mountains are 
formed of huge masses of stone, without any 
regular fissures, and are mostly homogeneous. 
They consist chiefly of granite, sometimes 
gneiss, schist us, flag-stone, sand-stone, lime- 
stone, gypsum, porphyry, or trap. Some in 
Sweden and Norway consist of iron ore. 
The stratified mountains are those whose 
mass is regularly divided by joints or fissures: 
these are called horizontal, rising, or dipping. 
Homogenous stratified mountains consist 
chiefly of stones of the argillaceous genus, or 
of the fissile compound species of the siliceous 
genus, as metallic rock ; sometimes of lime- 
stone of a granular or scaly texture, in which 
no animal vestiges appear. This limestone 
reposes on the argillaceous or siliceous strata: 
sometimes the argillaceous are covered with 
masses of granite, sometimes of lava. These 
mountains, particularly those of gneiss, me- 
tallic rock, and horn-stone, are the chief seat 
of metallic ores. When covered with lime- 
stone, the ore is generally between the lime- 
stone and the argillaceous stones. These 
ores run in veins, not in strata. Petrifactions 
are found upon, but not in, these mountains. 
Heterogeneous, or compound stratified 
mountains, consist of alternate strata of va- 
rious species of stones, earths, sands, &c. 
The limestone here is always of the laminar, 
and not of the granular or scaly, kind ; and 
when it contains any ore, it is placed between 
its laminae. Stones of the siliceous genus 
seldom form strata in these mountains, ex- 
cept lavas ; but the strata are frequently in- 
terrupted by siliceous masses, as jasper, 'por- 
phyry, &c. Coal, bitumen, petrifactions, 
and organic impressions, are found in these 
mountains; also salts and calamine. 
There are other mountains, which cannot 
properly be called stratified, as they consist 
only of three immense masses, the lowest 
granite, the middle argillaceous, and the up- 
per limestone. Metallic ores are found w 
6 
