The meaning of the term "value" in Art has already been explained

In painting landscapes from nature, two most important things to be considered are the study of the Values and Comparative Measurement.

The meaning of the term "value" in Art has already been explained, and too much care can not be given in thus ascertaining the relations of each tone to its surroundings.

The practice of comparative measurement consists of establishing some one object in the picture as a standard of measurement by which all other objects are compared, in order to ascertain their relative height, breadth or thickness.

For instance, take a tree in the middle distance and compare the size of its trunk with the trunks of trees in the foreground, and see how much larger the latter appear, though in reality the same size.