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<hi rend="smallcaps">Uniform</hi> <hi rend="italics">Matter,</hi> in Natural Philosophy, is that which is all of the same kind and texture.

</div1><div1 part="N" n="UNISON" org="uniform" sample="complete" type="entry"><head>UNISON</head>, in Music, is when two sounds are exactly alike, or the same note, or tone.

What constitutes a Unison, is the equality of the number of vibrations, made in the same time, by the two sonorous bodies.

It is a noted phenomenon in music, that an intense sound being raised, either with the voice, or a sonorous body, another sonorous body near it, whose tone is either Unison, or octave to that tone, will sound its proper note Unison, or octave, to the given note. The experiment is easily tried with the strings of two instruments; or with a voice and harpsichord; or a bell, or even a drinking glass.

This phenomenon is thus accounted for: one string being struck, and the air put into a vibratory motion by it; every other string, within the reach of that motion, will receive some impression from it: but each string can only move with a determinate velocity of recourses or vibrations; and all Unisons proceed from equal vibrations; and other concords from other proportions of vibration. The Unison string then, keeping equal pace with the sounding string, as having the same measure of vibrations, must have its motion continued, and still improved, till at length its motion become sensible, and it give a distinct sound. Other concording strings have their motions propagated in different degrees, according to the frequency of the coincidence of their vibrations with those of the sounded string: the octave therefore most sensibly; then the 5th; after which, the crossing of the motions prevents any effect.

This is illustrated, as Galileo first suggested, by the pendulum, which being set a-moving, the motion may be continued and augmented, by making frequent, light, coincident impulses; as blowing on it when the vibration is just finished: but if it be touched by any cross or opposite motion, and that frequently too, the motion will be interrupted, and cease altogether. So, of two Unison strings, if the one be forcibly struck, it communicates motion, by the air, to the other; and both performing their vibrations together, the motion of that other will be improved and heightened by the frequent impulses received from the vibrations of the first, because given precisely when the other has finished its vibration, and is ready to return: but if the vibrations of the chords be unequal in duration, there will be a crossing of motions, more or less, according to the proportion of the inequality; by which the motion of the untouched string will be so checked, as never to be sensible. And this we find to be the case in all consonances, except Unison, octave, and the fifth.

</div1><div1 part="N" n="UNIT" org="uniform" sample="complete" type="entry"><head>UNIT</head>, <hi rend="smallcaps">Unite</hi>, or <hi rend="smallcaps">Unity</hi>, in Arithmetic, the number one, or one single individual part of discrete quantity. See <hi rend="smallcaps">Number.</hi>—The place of units, is the first place on the right hand in integer numbers.

According to Euclid, Unity is not a number, for he defines number to be a multitude of Units.

</div1><div1 part="N" n="UNITY" org="uniform" sample="complete" type="entry"><head>UNITY</head>, the abstract or quality which constitutes or denominates a thing <hi rend="italics">one.</hi>

</div1><div1 part="N" n="UNIVERSE" org="uniform" sample="complete" type="entry"><head>UNIVERSE</head>, a collective name, signifying the assemblage of heaven and earth, with all things in them.

The Aneients, and after them the Cartesians, ima- <cb/> gine the Universe to be infinite; and the reason they give is, that it implies a contradiction to suppose it finite or bounded; since it is impossible not to conceive space beyond any limits that can be assigned it; which space, according to the Cartesians, is body, and consequently part of the Universe.

UNLIKE <hi rend="italics">Quantities,</hi> in Algebra, are such as are expressed by different letters, or by different powers of the same letter. Thus, <hi rend="italics">a,</hi> and <hi rend="italics">b,</hi> and <hi rend="italics">a</hi><hi rend="sup">2</hi>, and <hi rend="italics">ab</hi> are all Unlike quantities.

<hi rend="smallcaps">Unlike</hi> <hi rend="italics">Signs,</hi> are the different signs + and -.

UNLIMITED or <hi rend="italics">Indeterminate Problem,</hi> is such a one as admits of many, or even of infinite answers. As, to divide a given triangle into two equal parts; or to describe a circle through two given points. See D<hi rend="smallcaps">IOPHANTINE</hi>, and <hi rend="smallcaps">Indeterminate.</hi>

VOID <hi rend="italics">Space,</hi> in Physics. See <hi rend="smallcaps">Vacuum.</hi>

</div1><div1 part="N" n="VOLUTE" org="uniform" sample="complete" type="entry"><head>VOLUTE</head>, in Architecture, a kind of spiral scroll, and used in the Ionic and Composite capitals; of which it makes the principal characteristic and ornament.

</div1><div1 part="N" n="VORTEX" org="uniform" sample="complete" type="entry"><head>VORTEX</head>, or <hi rend="italics">Whirlwind,</hi> in Meteorology, a sudden, rapid, violent motion of the air, in circular whirling directions.

<hi rend="smallcaps">Vortex</hi> is also used for an eddy or whirlpool, or a body of water, in certain seas and rivers, which runs rapidly round, forming a sort of cavity in the middle.

<div2 part="N" n="Vortex" org="uniform" sample="complete" type="subentry"><head><hi rend="smallcaps">Vortex</hi></head>, in the Cartesian Philosophy, is a system or collection of particles of matter moving the same way, and round the same axis.

Such Vortices are the grand machines by which these philosophers solve most of the motions and other phenomena of the heavenly bodies. And accordingly, the doctrine of these Vortices makes a great part of the Cartesian philosophy.

The matter of the world they hold to have been divided at the beginning into innumerable little equal particles, each endowed with an equal degree of motion, both about its own centre, and separately, so as to constitute a fluid.

Several systems, or collections of this matter, they farther hold to have been endowed with a common motion about certain points, as common centres, placed at equal distances, and that the matters, moving round these, composed so many Vortices.

Then, the primitive particles of the matter they suppose, by these intestine motions, to become, as it were, ground into spherical figures, and so to compose globules of divers magnitudes; which they call the matter of the second element: and the particles rubbed, or ground off them, to bring them to that form, they call the matter of the first element.

And since there would be more of the first element than would suffice to fill all the vacuities between the globules of the second, they suppose the remaining part to be driven towards the centre of the Vortex, by the circular motion of the globules; and that being there amassed into a sphere, it would produce a body like the sun.

This sun being thus formed, and moving about its own axis with the common matter of the Vortex, would necessarily throw out some parts of its matter, through the vacuities of the globules of the second element constituting the Vortex; and this especially at such places as are farthest from its poles; receiving, at the same time,