Elevations, whether one or several, must always be taken at right angles to the plan. Although commonly, in simple work, confined to representations of each side or end, they can be taken from any point of view that may be at right angles to the plan. They may be taken from the corners or at any angles that may best show any complicated details of the object. If the object is quite simple, one elevation and the plan, or two elevations without the plan, may be quite sufficient, as the elevation or plan omitted can in such cases be understood at once.

Always make your drawings full-sized when the object to be made is not too large. You are much less likely to make mistakes in taking your dimensions and measurements from a drawing the actual size of the object than where you have to take them from a smaller drawing, and you also can get a better idea from a full-sized drawing just how the object will look. It is a safeguard, with a drawing which is symmetrical, to lay it out from a centre line, measuring to the right and left.

If you make a drawing of which each line is one half the length of the same line in the real object, it is called a "half-size" drawing, and is said to be drawn on a scale of 6" to the foot. If "one fourth size," the scale is 3" to the foot. The scale is often expressed as an equation, viz.: 2 in. = 1 ft., or 1/4" = 1".

If the drawing is not made with accuracy, it is necessary to put the dimensions upon it, and this is often done for convenience and quickness of execution in the case of drawings which are accurate.

Details inside of an object, that is, such parts as cannot be seen or properly shown in the elevations or plan, are often shown by dotted lines, as in Fig. 597. Sometimes dotted lines are used in the same way to show the back of an object, to save making extra drawings. Too many dotted lines, however, are confusing, so if the parts that do not show on the surface are not quite simple and cannot be clearly shown by dotted lines on the plan and elevations, it is usual to make another kind of drawing especially to show such details. This is called a "section" (Lat., sectio, from secare, to cut), and represents what would be shown if the object were cut apart or sawed through at the place where the view of the details is wanted. The surface supposed to be cut is usually indicated by parallel lines crossing the surface, independent parts, as those of different pieces, frequently being shown by changing the direction of the parallel lines, as in Fig. 5°4When both sides of an object are alike, labour and space are often saved by making a drawing of one side or one half only, from a centre line. The same way is sometimes adopted in making sections, and an elevation and section can sometimes be combined in this way in one drawing.

As soon as you become used to plans and elevations, you can by combining the plan and elevations in your mind quickly imagine the form of the object represented, and often, unless it is complicated, get fully as good a conception of it as from a picture, and a more accurate knowledge of its proportions and details, so that in many cases there is no need of having a picture at all in order to construct the object. It is often a convenience to have a picture, however, and frequently an assistance in forming a correct idea of something you have never seen. Where the appearance of the object is of consequence, as in the case of a house or bookcase, for instance, the picture is of the first consequence, for you must have a correct representation of the general appearance of the object before you begin to make the working-drawings. You will soon find that merely having an idea in your mind is not always sufficient from which to make working-drawings, although the first step in the process. You will often find that when the idea in your mind is put into the form of a picture, it does not look at all as you thought it would, and that if you had started at once on the working-drawings without first making a sketch or picture, the result would have been unsatisfactory and sometimes entirely impracticable.

Even making a sketch or picture that just expresses your idea will not always result in the completed object being just what you wish. Strange though it may seem, it is a fact, practically, that the completed object often looks quite different from what the sketch leads you to expect. That result, however, is something which cannot be helped, so you need not give it any attention, only do not be surprised if once in a while you find that what you have made is not just what you thought it would be. First make the best design you can, then accurate working-drawings, then work carefully by the drawings, and if the result is not always exactly what you expected, you can console yourself with the thought that your experience is only that of architects, designers, carpenters, and workmen in all lines, and that no one can foresee all the conditions by which a piece of projected work will be affected.

Oblique or parallel projections are often used, from which measurements can be made. Such projections are not true representations of the objects as they appear to the eye, but they are often used because readily understood and easily drawn. They often answer every purpose from a practical point of view. Figs. 120 and 344 are examples.

Another way of representing objects for practical purposes is that shown in Figs. 121 and 407, and known as "isometric ' projection" or ""isometric perspective." This method is incorrect so far as giving an accurate picture is concerned, for the object is always represented as being too large in the farther parts, because the inclined lines are drawn parallel instead of converging; but it is often very useful from a practical point of view, because by it all that is required can frequently be expressed in one drawing.

Isometric perspective will not readily give the correct dimensions except in the lines which are vertical or which slant either way at an angle of 300 with the horizontal, - i. e., you cannot take the other dimensions right off with a rule as from a plan, and therefore, so far as obtaining correct dimensions is concerned, it is practically not useful for other than rectangular objects; but so far as merely showing the general shape or conveying the idea of the form it can often be advantageously used in representing many objects containing curved lines. Isometric projection has the advantage of being easy of execution, and of being so pictorial that it is almost always easy to see what is meant.

1 Gr., equal measure.