ualities present themselves as just what they are, stati- cally demarcated from one another. Moreover, they rarely change, when left to themselves, in such ways as to indicate the interactions or relations upon which their occurrence de- pends. No one ever observed the production of the thing having the properties of water, nor the mode of generation of aflash of lightning. In sensory perception the qualities are either too static or too abruptly discrete to manifest the specific connections that are involved in their coming into existence. Intentional variation of conditions gives an idea of these connections.