The book is not a treatise. It purports only to give an intro-duction to physical principles underlying design, illustrated by calculations, and by graphical techniques appropriate to the drawing-board. Of necessity several interesting subjects-such as network calculations for conditions of fault-are omitted, chiefly because the graphical work is small and not because they are considered in any way unsuitable for inclusion in a design course. The material is intended for students rather than for designers and specialists, and requires support by courses of lectures or of wider reading in the subjects dealt with.