period of time the simplest and most rudimentary forms, and at another the most complex and highly organized; we cannot do otherwise than conceive these two extremes as related by intermediate terms, through the operation of some law which holds good throughout the series. The relation subsisting between any two, must be the same as that subsisting between any other two similarly situated, or a departure from that relation which is itself governed by a definite law discoverable from a comparison of two sets of terms. The application of this law is so universal and so rigid that we need not hesitate to interpolate a missing term, and confidently assert that it either does exist or has existed. To deny this principle is to deny the necessity of continuity in reasoning. This continuity of thought is represented in matter by the persistence of generic forms under specific differences. But just as the specific is the generic with certain additions, so the individual is this same generic with still further additions; and these additions, whether considered solely in space, as given in the symbols of physical science, or in time as in the conceptions of intellectual science, must be determined by the same unvarying law. The persistence of the same form furnishes us the means of identifying this relation, while the differences reveal to us the successive steps by which the generic was differentiated into the individual. If the creative thought has been expressed by the forms of matter, the laws of thought must be thus expressed in the relative forms of matter. Anything less than this, while it might interpret isolated ideas, would not communicate the method of the creative process, and science is nothing but the discovery of this method. If the terms of the logical process must be arranged in a series, the physical symbols rendering this logical process cognizable, must be arranged in a similar series, for science becomes impossible when the logical process becomes undiscoverable.