[Footnote 16: Yves Delage: Physiol. Studien über d. Orientirung (Aubert's transl.), p. 100, Tübingen, 1888.] [Footnote 17: E. B. Holt: Harvard Psych. Studies, Psych. Rev. Mon. Supplements, vol. 4, p. 1, 1903.] [Footnote 18: E. Mach: Analyse der Empfindungen, 2d ed., p. 98, Jena, 1900.] [Footnote 19: R. Dodge: Amer. Jour. of Physiology, vol. 8, p. 317, 1903.] [Footnote 20: E. B. Holt: Harvard Psych. Studies, Psych. Rev. Mon. Supplements, vol. 4, p. 42, 1903.] [Footnote 21: S. Exner: Zeitschrift für Psych. u. Physiol., vol. 1, p. 46, 1890; E. Fick and A. Gürber: Berichte d. ophth. Gesellschaft in Heidelberg, 1889; E. B. Holt: _op. cit._ p. 4.] [Footnote 22: Purkinje, 1825; reprinted in Aubert's Physiol. Stud. über d. Orientirung, p. 117, Tübingen, 1888.] VISUAL IRRADIATION BY FOSTER PARTRIDGE BOSWELL There are various kinds of visual irradiation, of which perhaps the best-known variety is that which appears as the enlargement of a brightly illuminated surface at the expense of a contiguous one of less intensity. This has been until recently the only form recognized, and until very lately the greater part of the literature has dealt with it alone. The whole subject was carefully investigated by Plateau in 1831, and retinal irradiation extricated from phenomena which very often accompany it. He showed that the extent of irradiation varies with the intensity of the stimulating light and the time during which it is allowed to act. He was also the first to call attention to the phenomenon of so-called negative irradiation. Somewhat later Volkman again called attention to negative irradiation, while Aubert, in opposing the explanation advanced by Volkman, first showed the relations existing between irradiation and contrast. Dove was the first to investigate the influence of irradiation on stereoscopic pictures, thus calling attention to the question of binocular irradiation. Experiments in this direction, however, have in general given negative results in so far as any enlargement of the binocular portion is concerned. Helmholtz examined the manner in which the stimulation at the border-line between a light and dark field changes in intensity, and drew a curve showing these modifications of intensity due to irradiation. Hering showed that the form of the Helmholtz intensity curve would be modified by the presence of other phenomena not strictly those of irradiation. De Roux demonstrated the difference in the extent of a real induction on the foveal and the extra-foveal parts of the retina.