The dividers, or compasses, are constructed in various ways, but the so-called wing dividers are found in most shops. (See Fig. 15.) They are used:

1. To lay out circles or arcs of circles.

2. To space off equal distances.

3. To scribe lines parallel to an irregular edge or surface.

Wing Dividers.

Reference Work: Look up:

Trammels, calipers, level, plumb-bob, use of chalk line.

Topics for home study: Look up and try to construct apparatus to measure (a) temperature, (b) time, (c) steam pressure, (d) quantity of liquids, (e) density of liquids. Try to make a balance to weigh (1) ounces accurately, (2) pounds accurately, (a) up to 10 lbs., (b) up to 200 lbs.