Previously I have described three tests1 for binocular stereopsis, each of which utilizes one or more new principles. These tests are essentially, only qualitative, although the kinetic test, the most useful of the three, does permit acuity to be estimated with considerable accuracy. About five years ago I devised a test based on an entirely different principle, that of presenting misleading monocular criteria so as to make binocular parallax the only correct evidence of relative depth and to cause perception of false depth when this correct evidence was not perceived. So far as I am aware this principle had never before been purposely employed. During the past year I have made the test accurately quantitative. One of its important advantages is that it reduces to a negligible factor the possibility of correct guessing. The test is simple and is made without the use of a stereoscope, amblyoscope or, in