“This collection of blackboard sketches and the accompanying text has been planned at the request of many teachers and pupils who desire lessons and suggestions along this line, but who are unable to secure personal instruction. In general, these requests have been for simple sketches dealing with the various lines of school work, and at the same time for strokes and explicit directions for using these in the drawings. For these reasons there are given upon nearly every plate the strokes of the chalk useful in producing the desired effect, and upon the opposite page such directions as are generally given to the students in the classroom. ” Это и многое другое вы найдете в книге Blackboard Sketching (Illustrated Edition) (Dodo Press) (Frederick Whitney)