goes to the ends of the earth and photographs a solar eclipse, making all sorts of measurements and calculations, we may say that this is an observation and not an experiment, but we have not made a useful definition; neither do we gain anything by deciding whether it is an experiment when a baby pulls apart a doll to see what is inside. The real distinction is between the casual experimenting and observing of daily life, and the planned and purposive experiment and observation of science. Science is experimental qua science.
I consequently object to making experimental psychology a branch of psychology. It is a method in psychology, which is extended just as rapidly as psychology becomes a science. The purely introspective or analytic observer does, according to the current definition' continually make experiments, because his introspection itself alters the process that he is observing, thus sometimes making his observations invalid as a description of natural conditions. On the other hand, the student in the laboratory may measure the process without any introspection or interference with it, and this may not be technically an experiment at all, but it gives a scientific description of the normal course of mental life. We are told that Adam gave a very appropriate name to the hog; science is not always so fortunate in its nomenclature.
Most experiments, letting experiments mean attempts to increase scientific knowledge, are also measurements. Measurement is only a description; but it has proved itself to be the most economical, wide-reaching and useful form of description. What language was for the evolution of primitive man, measurement is for the advance of modern science. As a word selects similarities and ignores differences, so a measurement selects certain similarities from the concrete manifoldness of things. That such a great part of the world can be described in terms of a few units of measurement, and that this description should lead to such useful applications, is truly marvelous and admirable. As I am writing these paragraphs, I have received a manuscript in which the author explains that the fact that the earth rotates on its axis in twenty-four hours, not varying a second from day to day, is a conclusive proof that it was created and set rotating by a benevolent being. If the days were shorter, he says, we could not get our work done, and if the days were longer, we should be too tired by night. It almost seems as though the world were made in such comparatively rational fashion in order that we may measure it.
The physicist counts, and he measures time, space and energy. He has intractable matter with its seven and seventy elements, and he may come across a substance as complex and perplexing as radium. But by and large he can describe his world in certain quantitative formulas. It is true that he accomplishes this in part by unloading on psychology qualitative differences, such as colors and tones. So much the
