§ 13. Emotions. 197 as checks for experimental introspection the expressive move- ments have great value. The principle that observation is wholly inadequate when applied to psychical processes which present themselves in the natural course of life, holds especially for the emotions. In the first place, emotions come to the psychologist by chance, at moments when he is not in a con- dition to subject them to scientific analysis; and in the second place, in the case of strong emotions which arise from real causes, we are least of all able to observe ourselves with exactness. Exact observation can be carried on much more successfully when we voluntarily arouse in ourselves a particular emotional state. In such a case, however, it is not possible to estimate how nearly the subjectively aroused emotion agrees in intensity and in mode of occurrence with one of like character due to ex- ternal circumstances. For this reason the simultaneous investiga- tion of the physical effects, especially of those effects most re- moved from the influence of the will, namely the effects on the pulse and respiration, furnishes a check for introspection. For when the psychological quality of emotions is alike, we may infer from their like physical effects that their formal attributes also agree. Indeed, the intensity of the expressive movement furnishes a fairly reliable measure of the degree in which the artificial emotion approximates the natural emotion. References. Kant, Anthropologie, Bk. 3. Darwin, The Ex- pression of the Emotions, 1872. Piderit, Mimik und Physiogno- mik, 2nd ed. 1866. Hughes, Die Mimik des Menschen, 1900. Lehmann, Die koerperlichen Aeusserungen psychischer Zustande, vol. I, 1899. W. Gent, Volumpulskurven bei Gefuehlen und Af- fekten, Phil. Stud., vol. 18. Mosso, (English trans, by Kiesow), On Fear. Wundt, Voelkerpsychologie, vol. I, pt. i.chap. i. James, Principles of Psychology, vol. II, chap. 25. Wundt, Zur Lehre von den Gemuetsbewegungen , Phil. Stud., vol. 6 (contains also a criticism of the various theories.
8. The great number of factors which must be taken into consideration for the investigation of emotions renders a psychological analysis of the single forms impossible. This is all the more so because each of the numerous distin- guishing names marks off a whole class, within which there is a great variety of special forms, including in turn an end-
