Art critics today are concerned with certain modern developments to which they have attached the borrowed term of fourth dimension, and although the world of art is, in most senses, far removed from the Theory of Relativity, there is nevertheless an interesting analogy, since both are directly concerned with space and time. From scientists we learn that space and time are not to be thought of as independent aspects of nature but one, and for this union of elements we have the expression space-time. According to authorities in esthetics a parallel condition prevails in art. Space and time have their effect in a unified way in the enjoyment of any work of art. Moreover, in ordinary experience perception takes place in a similar manner. Thus the presence of space-time in art as well as in practical affairs is not new; it has been with us from the beginning.