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RUPERT DEAKIN, M.A.,
HEADMASTER OF KING EDWARD'S GRAMMAR SCHOOL, STOURBRIDGE.
INTRODUCTORY COURSE OF DRAWING AND MEASUREMENT;
AND PROBLEMS ON PRACTICAL GEOMETRY.
Third Impression (Second Edition).
LONDON: W. B. CLIVE,
Unibersity. Tutorial (Prebs L.
(University Correspondence College Press),
INTRODUCTORY COURSE OF DRAWING AND
The instruments required in this course are compasses, a flat ruler, set squares, and a protractor; dividers and parallel rulers will also be found useful. The ruler should have a scale of inches and tenths of an inch on one edge, and a scale of millimetres on the other edge.
Numerical answers are given in many cases to three significant figures, but with these instruments the third figure can seldom be estimated correctly.
In many of the problems it may be advisable for the teacher to help the class by rough sketches on the board.
1. The student must first learn the meanings of the words circle, centre, radius, diameter, triangle, base, side, vertex. See Definitions 15, 16, 17, and 21 on pages 4 and 6. Look at the different shapes of the triangles on page 6.
We shall frequently use the symbol A for triangle, and the symbol " for inches ; also the abbreviations cm. and mm. for centimetres and millimetres.
Problem I.—To construct a triangle, given its three sides.
Construct a triangle having its base 2 inches long, its left side
с 1 inch long, and its right side 1.6 inches long.
16" Draw the base AB of length
A 2" B 2 inches [Fig. 1]. Describe a circle with centre A and radius 1 inch. Describe a circle with centre B and radius 1.6 inches. Take the point C above AB where
Fig. 1. the circles cut one another, and join it to A and B by straight lines. ABC will be the required triangle.
For the side AC is a radius of the left hand circle and is therefore 1 inch long; and the side
16" BC is a radius of the right hand circle and is therefore 1.6 inches long.
B It is not necessary to draw the complete circles, but only the parts of the circles (or “arcs”') in the neighbourhood of the point c. See Fig. 2.
Note that by turning a triangle round we may regard any side as the base.