Page:Popular Science Monthly Volume 51.djvu/111

Rh It is to be noted that these statements refer to investigations of and speculations on the brain for psychological purposes. For physiological purposes the case is utterly different. The development of brain anatomy and of the knowledge concerning the localization of cerebral functions are among the greatest achievements of modern time.

Moreover, the collection of facts and the development of theories of the nervous activities accompanying mental phenomena has given rise to the science of physiological psychology.

With these sciences, however, the psychologist has comparatively little to do. The study of brain function has not contributed a single fact to our knowledge of mental life; the deductions of physiological psychology concerning nervous function have begun with the facts of experimental and observational psychology, and are still so unsettled as not to allow additional deductions backward.

While this was going on, physics had through Helmholtz, Mach, and others gradually come to a clear understanding of the relation of its facts to the immediate facts of consciousness. Direct experience as present in our sensations was accepted as supplying the facts of physics. For example, in measuring the length of a bar, a visual sensation, the scale of measurement, was applied to another visual sensation, the bar. Indeed, as was clearly recognized, every direct measurement of physics was primarily a comparison between sensations—in other words, a psychological measurement. From this combined measurement the physicist reduced as much as possible the psychological elements; it was but a step for the psychologist to reduce the physical elements in order to have a psychological measurement. This step made psychology for the first time a science in the