VAU 
metals ; some of which are blue, almost 
as beautiful as the turquoise ; others with an 
inimitable vermilion colour ; others with a 
certain shining polished brown, vastly finei 
than Brasil figures. 
The most usual varnish is a beautiful 
green, which hangs to the finest strokes with- 
out effacing them, more accurately than the 
finest enamel does on metals. No metal but 
brass is susceptible of this ; for the green rust 
that gathers on silver always spoils it, and it 
mustbe got off with vinegar or lemon-juice. 
Falsifiers of medals have a false or modern 
varnish, which they use on their counterfeits, 
to give them the appearance, or air, of being 
antique. But this may be discovered by its 
softness, it being softer than the natural var- 
nish, which is as hard as the metal itself. Some 
deposit their spurious metals in the earth for 
a considerable time, by which means they 
contract a sort of varnish, which may impose 
upon the less knowing ; others use sal ammo- 
niac, muriat of ammonia, and others burnt 
paper. 
VARRONIA, a genus of plants of the 
class and order pentandria monogynia. The 
corolla is five-cleft; drupe with a four-celled 
nut. There are nine species, shrubs of the 
West Indies. 
VASSAL, in old law-books, denotes a te- 
nant that held in fee of his lord, to whom he 
vowed fidelity and service. 
VATERIA, a genus of the polyandria 
monogynia class of plants, the flower of which 
consists of five oval and patent petals ; and 
its fruit is a turbinated, coriaceous, and uni- 
locular capsule, containing a single oval seed. 
There is one species. 
VATIC A, a genus of the dodecandria mo- 
nogynia class and order of plants. 1 he ca- 
lyx is five-cleft; petals five; anthers 15, 
sessile, four-celled. There is one species, a 
tree of China. 
VAULT, in architecture, an arched 
roof, so contrived that the stones which 
form it sustain each other. Vaults aie, on 
many occasions, to be preferred to soffits or 
\ ceilings, as they give a greater height and 
|! elevation, and are besides more firm and 
durable. , 
Salmasius observes, that the antients had 
only three kinds of vaults. The first was the 
fornix, made cradle-wise ; the second a tes- 
tudo, i.e. tortoise-wise, which the French 
call eul de four, or oven-wise; and the third 
! concha, or trumpet-wise. Bwt the moderns 
have subdivided these three sorts into many 
more, to which they have given different 
names, according to their figures and uses ; 
gome of them are circular, and others ellip- 
tical. 
Again, the sweeps of some are larger, 
others less, portions of a sphere. All such 
as are above hemispheres are called high, or 
surmounted vaults ; and all that are less than 
hemispheres, are called low, or surbased 
vaults, or testudines. 
In some vaults the height is greater than 
the diameter ; in others it is less ; others 
a aain are quite flat, and only made with 
haunses ; others like ovens, or in the form of 
a cul de four, &c. and others growing wider 
as they lengthen, like a trumpet. 
Vaults, master, are those that cover the 
principal parts of buildings, in contradistinc- 
tion to the upper or subordinate vaults, which 
4 
VAU 
only cover some little part, as a passage or j 
gate, &e. 
Vault, double, is one (hat is built over 
another, to make the outer decoration range 
with the inner ; or, to make the beauty and 
decoration of the inside consistent with that 
of the outside, leaves a space between the 
concavity of the one and the convexity of 
the other ; instances of which we have in 
the dome of St. Peter’s at Rome, St. Paul’s 
at London, and in that of the Invalids at 
Paris. 
Vaults with compartments, are such 
whose sweep, or inner face, is enriched with 
pannels of sculpture, separated by platbands. 
These compartments, which are of different 
figures according to the vaults, and usually 
gilt on a white ground, are made with stone 
or brick walls, as in the church of St. Peter 
at Rome, or with plaister on timber vaults. 
Vaults, theory of. A semicircular arch 
or vault, standing on two piedroits, or im- 
posts, and all the stones that compose them, 
being cut, and placed in such manner as that 
their joints or beds, being prolonged, do all 
meet in the centre of the vault ; it is evident 
that all the stones must be in the form of 
wedges, i. e. must be wider and bigger at top ; 
by means of which they sustain each other, 
aud mutually oppose the effort of their 
weight, which determines them to fall. The 
stone in the middle of the vaults, which 
stands perpendicular to the horizon, and is 
called the key of the vault, is sustained on 
each side by two contiguous stones, just as by 
two inclined planes ; and, consequently, the 
effort it makes to fall is not equal to its 
weight. But still that effort is the greater, 
as the inclined planes are less inclined ; so 
that if they were infinitely little inclined, 
i.e. if they were perpendicular to the horizon 
as well as the key, it will tend to fall with its 
whole weight, and would actually fall but 
for the mortar. The second stone, which is 
on the right or left of the key-stone, is sus- 
tained by a third, which, by virtue of the 
figure of the vault, is necessarily more inclin- 
ed to the second than the second is to the 
first ; and consequently the second, in the 
effort it makes to fall, employs a less part of 
its weight than the first. For the same rea- 
son, the stones from the key-stone employ 
still a less and less part of their weight to the 
last; which, resting on a horizontal plane, em- 
ploys no part of its weight, or, which is the 
same thing, makes no effort at all, as being 
entirely supported by the impost. Now, in 
vaults, "a great point to be aimed at is, that all 
the voussoirs, or key-stones, make an equal 
effort towards falling. To effect this, it is 
visible, that as each (reckoning from the key 
to the impost) employs still a less and less 
part of its whole weight ; the first, for in- 
stance, only employing one-half ; the second, 
one third ; the third, one-fourth, &c. there 
is no other way of making those different 
parts equal, but by a proportionable augmen- 
tation of the whole ; i. e. the second stone 
must be heavier than the first, the third than 
the second, &c. to the last ; which should be 
infinitely heavier.. 
M, De la Hire demonstrates what that 
proportion is, in which the weight of the 
stones of a semicircular arch must be increas- 
ed to be in equilibrio, or to tend with equal 
forces to fall, which is the firmest disposition 
a vault can haye. The architects before him 
V E L 847 
had no certain rule to conduct themselves by, 
but did all at random. Reckoning the de- 
grees of the quadrant of a circle, from the 
key-stone to the impost, the extremity of 
each stone will take up so much the greater 
arch as it is farther from the key. 
M. De la Hire’s rule is, to augment the 
weight of each stone above that oi the key- 
stone, as much as the tangent of the arch ol 
the stone exceeds the tangent of the arch of 
half the key. Now the tangent of tlu: last; 
stone of necessity becomes infinite, and of 
consequence its weight should be so too ; 
but, as infinity has no place in practice, the 
rule amounts to this, that the last stones 
should be loaded as much as possible, that 
they may the better resist the effort which 
the vault makes to separate them; which is 
called the shoot or drift of the vault. Mr. 
Parent has since determined the curve, or 
figure, which the extrados, or outside of a 
vault, whose intrados, or inside, is spherical, 
must have, that all the stones may be in. 
equilibrio. 
Vault, key of, is a stone or brick in the 
middle of the vault, in form of a truncated, 
cone, serving to bind or fasten all the rest. 
U B IQU I' PARIAN S, in church-history, 
a sect of heretics who sprung up in Germany 
about the year 1590, and maintained that the 
body of Jesus Christ is ubique, every where, 
or in every place, at the same time. Flow- 
ever, they were not quite agreed among 
themselves ; some holding, that the body of 
Jesus Christ, even during his mortal life, was 
every where ; and others dating the ubiquity 
of his body from the time of his ascension 
only. 
VECTOR, in astronomy, a line supposed* 
to be drawn from any planet moving round a. 
centre, or the focus of an ellipsis, to that, 
centre or focus. 
VEER, a sea-term variously used. Thus 
veering out a rope,. denotes the letting it go 
by hand, or letting it run of itself. It is not 
used for letting out any running rope except- 
the sheet. 
Veer is also used in reference to the wind; 
for, when it changes often, they say it veers 
about. 
VEGETATION. See Plants, physi- 
ology of 
VEIN. See Anatomy. 
Vein, among miners, is that space which 
is bounded with woughs, and contains ore,, 
spar, canck, clay, chirt, croil, brownhen, 
pitcher-chirt, cur, which the philosophers call 
the mother of metals* and sometimes soil of 
all colours. When it bears ore, it is called a 
quick vein ; when no ore, a dead vein. 
VELEZIA, a genus of the pentandria di- 
gynia class and order of plants. The calyx 
is filiform, five-toothed; corolla five-peta lied, 
small; capsules one-celled ; seeds numerous. 
There is one species. 
VELLA, a genus of the tetradynamia si- 
liculosa class of plants, with a tetrapetalous 
cruciform flower ; the stamina are six fila- 
ments, about the length of the cup ; and the 
fruit is a globose, cristated, bilocular pod, 
containing a few roundish seeds. There are 
two species. 
VELVET, a rich kind of stuff, all silk, 
covered on the outside with a close, short, 
fine, soft shag, the other side being a very 
strong close tissue. The nap or shag, called 
also the velveting, of this stuff, is formed of 
