DIMENSION (from the Latin) a principal distance mea sured in a straight line on the surface of it body, in some particular direction. or through some certain point, by the help of which the body may be constructed or measured as to its superficial or solid contents.

The dimensions of rectangular figures and solids are taken along, or parallel to the straight lines which bound their faces ; and consequently rectangles have two dimensions. length and breadth, and rectangular prisms three dimensions, viz. length, breadth, and thickness. The dimension of a lelogram are the length of one side, and the distance from that side to the opposite side of the same, so that the two dimensions of a parallelogram are at right angles to each of any plane figure are the lengths of the sides and diagonals. The dimensions of a circle are its /adios, diameter, or circumference, or all. The dimensions of a regular polygon are the length of one of its sides, and their number. The dimensions of any prism are the ditnen si ors of one of its ends or bases, and the perpendicular or distance between the said ends or The dimensions of :A pyramid are the dimensions of' its base, and the distance or perpondieula• form the apex to the plane of the base. The dimensions of it sphere are its diameter or eireninferenee.

The dimensions of a spheroid are the fixed and 'revolving axes. The dimensions of an irregular surface or body are in a great measure arbitrary. The dimensions of an irregular surface are thus taken : Fix upon some principal line passing through the middle of the body in the direction of its greatest extension, as nearly as can be judged ; then divide the length of this line into parts; through the points of division, draw perpendiculars, terminated by the boundary ; then the length of the first line and of the perpendiculars are the dimensions. The dimensions of a definite body may be limited as to number, and the body may be accurately ascer tained, either with regard to its construction or solidity ; hut an indefinite body can never he ascertained for either, what ever may be the number of its dimensions: greater accuracy, however, will be obtained, the greater the number of dimen sions taken. The dimensions of an irregular plane figure or

solid, ought to be taken in equidistant lines or planes.

The to which dimensions are applied belong to geometry, mensuration, anti the construction of solids. The method of squaring dimensions w ill be found under the articles Cross MULTIPLICATION, DECIMALS, and DUO DECIMALS.

In writing the dimensions of a body, consisting of many different parts, in order to avoid mistakes, an eye-draught, or sketch of the body, should be made, and two angles, each with its apex fixed in the opposite extremities: of' the exten sion, with a number placed between them to denote the length of the line: thus, 36 ft. denotes 36 feet between the point of one angle and that of' the other: the opening of each angie is always turned towards the centre of the line. By this method no mistake can oectir, even though ever so many other dimensions cross one another, unless they come so close as to confuse. Simple rectangles, or rectangular prisms, are most frequently written down without any eye-draught, and the dimensions entered in the book with a cross between each, or the word By ; thus, for a rectangle, 3.. 9'54 .. 8', or 3 .. 9' by 4 .. 6'; that is, 3 feet 9 inches by 4 feet S inches; the mark thus', signifying that the figures below are inches, and consequently that the first is the place of feet. A solid is thus denoted, 5 . 3' X 4 .. S' X 12.. 6', or 5 .. by 4 .. S' by 12 .. 6'; that is, the end. or base, is 5 feet 3 inches by 4 feet S inches, and 12 feet 6 inches from end to end ; or the solid is 12. feet 6 inches 1011g, 5 feet 3 inches broad, and 4 feet S inches thick.

In finding the contents of artificers' works in buildings, the dimensions are placed one under the other, according to their denominations, and the surtilee or solid is known by the number of its dimensions ; in order therefore to distinguish any set of dimensions from the next, whet her above or below, a horizontal line 'mist be drawn between them. See the article 1 srciswons.

DinussioN Bow:, a book in which the measurement of the builder's work is entered, speeimeus of which are given under the head Ilateu•om:.