Vision under water is attended with some peculiar consequences - the result of what is tormed "intemal " rcflcction. An eyc placod under perféctly still Water, as, for instanco, the eye of a diver, will seo oxternal objects only through a circular aperture, as it were, of il( degrees, 55 minutes and 22 seconds ! in diameter overhead. But all tb jee te down to the horizon will be visiblo iu this spacé - those noar the horizon being muoh distorted and contractcd in dimensions, espeoially in height. Beyond the limite of this circle will be seen the bottom of tho water, and all ! subaqueous objects reflected and as vividly depicted as by direct visión ; and, in addition, the circular space above mentioned will appenr surrounded with a rainbow of faint but delicate colors. In the eyes of fishes, the humors being nearly of the refraotive density of the medims in which they i livo, the action of bringing the rays to a focus on the retina is almost entirely performed by the erystalline lens, which is nearly spherical, and of email radius in comparison witli the wliole diameter of the eye.