COM

185

COM

til^° MPAR TMENT Tiles, an arrangement of white and red

Cb\r2 I8 “ e< *’ ^ or *' le decoration of the covering of a roof.

HEADED, having a semicircular head,other f >. ASS ■^ 00I '> that which extends from one wall to theits cent w k°le width of the building, having a ridge inr °of, ana®! J he term is used in contradistinction to lean-toroofg rp 13 peculiarly applied to the ancient open timberor b ’ ~he term is applied by some to roofs with cylindricalrrel vaults.

C 0 jJp Ass Saw. See Saw.

a bow Ass . Wj ndow, a window which has a circular plan ;

Cornel window.

■tistrub ^SSES, (from the French , compas ) a mathematicalalso f or ent ^ or describing circles and ellipses, or their arcs;

C ottl meas uring and proportioning distances,logs, lti * lasses for drawing are of four kinds: those with twoe *tend e 7 ea ld e on a joint, by which the extremities can beare Ca j, , to an y distance, not exceeding the sum of both legs,D . c °mmon compasses. Those with a beam having aai, otbg r nt . at one of its ends, and a moveable collar carrying$>* e d o ?° lnt > which may be fixed at any distance from the;So b , y means of a screw, are called beam compasses.n’H 2 , three le S S > so as to be set to any three points, ofe distance between any two may not be greater thanCa >n Pass 0t an y two logs °f the compass, are called triangular^Pass^l r fl 10se for drawing ellipses, are called elliptic

' v 'th com passes are of several kinds, and are furnished

C 0tnm or Woveable points, for carrying a pencil or ink foot.5ls, "nc es °^ Com passes with sharp points, used for taking

k°int of S> are Ca H e d dividers. Dividers, which have the lowera°n n / tbe l e S s fastened to the upper part by a stiffn e legs a by means of a screw will allow of slow motion in^ 8rt >all°. aS to exten d or shorten the distance of the points toev eable ?t degree, are called hair compasses. Those withfit 'n ari d pencil feet, for describing circular lines, are(I e <l i nto Contra distinction, compasses; the ink or pencil foot is' ,! k a a Soe 'ket in one of the legs of the compass. Besidest ait itig Pencil feet, there is sometimes another foot for8 a t\v 0 Q ^ u ar lines, but it is seldom used, as being apt toif 11 cit'd 1,1 ? re dots into one. Compasses for describing6 . Ca lleri *? ' v ’th ink or pencil, and which shut into a bow,

j 1 iing con

to t vl at ; like common compasses, and the third leg is

>n g £? iar compasses have two legs, which revolve on a

to

the K common compasses, ana tne tmra leg ism “fib by means of a projection, with a joint, soc oiDpa s ° Vea ble in every direction. The three points of^. Uta C(i j, , es may be made almost to coincide with any^hsion lllts > to any distance within the reach of

> ( 1 P ^ may be made almost to coincide with any three^ nts > to any distance within the reach of their

^V^^ses „ • v

U 1(i P Point 8 ' Vlt l a J olnt between the extremities, and twoeri( j at each end, forming a double compass, so thatpreserve the same ratio, howeverit tb e 6 Ca ll e d proportional compasses. When the jointa C ° ra P ass 1® said to be simple; but when moveable,sittip] C ° m P oun d proportional compass.

\ a l he tw e Proportional compasses, in most general use,th e ° e = s on one side of tbe centre always doublefeting otl| er, and are denominated wholes-and-halves,

c Ur a ^ lorir, ..Proportional compasses have each branch cutNio ‘ 8 ^scr 1 f ° r a cursor to slide in ; in the middle of theea e ,' v > by which the ends may be set in any pro-nto a of ot ^ er - One leg is generally graduated onkit slit, one side for the division of right lines

I ^kioij 6r e( l ua l parts from 2 to 10, and the other® P°lygons from 6 to 20 sides in a circle of any3 it

given radius within the greatest extension of the compasses.The other leg is graduated in a similar manner, one side intodivisions, showing the proportion between the areas of similarplane figures, the other into parts showing the proportionbetween the contents of similar solid figures. This instru-ment is employed in the reduction of figures, and is extremelyuseful in the projection of dome compartments, and inperspective.

Examples of the use of compound proportional compasses.—Let it be required to divide a straight line into four equalparts : push the cursor till the index be just on the figure 4,and fix it there; then take the length of the given line withthe longer legs, and the distance between the points of theother legs will be one-fourth of the length of the line.

Again, let it be required to inscribe a heptagon in acircle : push the cursor till the index or zero be on 7 ; then,with the longer legs take the radius of the circle, and thedistance between the two other points will be the side of theheptagon. See Projection.

To find a regular plane figure whose area shall equal one-fourth of that of a given similar figure; set the zero on thecursor to the line marked 4, take the length of one of the sidesof the given figure with the longer legs, and the distancebetween the points of the shorter ones will give the side ofa similar figure which shall contain an area equal to one-fourth af the area of the given figure.

By means of the same scale of divisions, may be found thesquare root of any given number, thus :—Set the zero of thecursor to the given number; open the longer legs so as tocontain the same number from any scale of equal parts, thenapply the points of the shorter legs to the same scale, andthe distance measured between them will give the square rootof the given number.

To find a sphere or cube whose solid contents shall be equalto one-fourth of those of a given sphere or cube: Set the zeroto the division marked 4, measure the diameter of the givensphere, or the side of the given cube, with the points of thelonger legs, and the points of the shorter ones will givethe diameter of a sphere or side of a cube such as required.

The cube root of any number may be found by this scalein a similar manner to that by which the square root is foundby the opposite one.

Compasses used in the description of ellipses, are calledelliptic compasses, or ellipsographs. See Ellipsograph andPentagraph.

COMPASSING (from the French , compasser, to encircle)in naval architecture, the act of bringing any piece of timberinto the form of an arch.

COMPLEMENT (from the Latin, complemenhtm, perfec-tion ) in a general sense, the full quantity, or completion ofanything.

Complement, in geometry, whatever is wanting of anyangle to make a right angle, or 90 degrees.

Complement of a Parallelogram, two lesser parallelo-grams, made by drawing two right lines parallel to the sidesof the greater parallelogram, through a given point in thediagonal.

COMPLU V1U M (Latin ) in ancient Roman buildings, issupposed by Newton to be the gutter of a roof; but byDr. Adam (Roman Antiquities') to be the aperture at the topof the cavsedium. See Cav^edium.

COMPOSITE ARCH, the pointed or lancet arch.

Composite Base, 1

Composite Capital, > See Roman Order.

Composite Order, }

COMPOSITION, the distribution and arrangement of the

component parts of an architectural design.