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The instruments at the disposal of the psychologist are those familiar to every psychological laboratory: the pneumograph, which registers the movements of respiration; the sphygmograph, which writes the pulsation of the artery in the wrist; the automatograph, or other instruments, which register the slight unintentional movements of the arm.

Here belongs also the ergograph, which gives the exact record of muscular work with all the influences of will and attention and fatigue, the automatograph which writes the involuntary movements, especially also the galvanoscope which may register the influence of ideas and emotions on the glands of the skin, and thus lead to an analysis of repressed mental states, and hundreds of other instruments which are used in the psychological laboratory.