been measured in its effects by man, and these measurements have rarely been definite enough to establish any exact equivalence. Yet the notion of causation, present as a term of interpretation quite interior to all phenomena, affirms itself as an exact and universal law of the physical world. It brings its own force to the nine hundred and ninety-nine facts, it does not derive it from them. The mental conceptions quite transcend in completeness the physical experiences to which they apply, --- or the mind's knowledge of those facts --- and are often coherently developed, as in geometry and logic, far in advance of physical inquiry. Nor have these truths been the slow deposit of the mass of minds under protracted experience, but a sudden uplift of thought in a few, dimly shared, if shared at all, by the many. The completeness and necessity of these mental ideas and laws quite distinguish them from the products of experience, from that knowledge which arises certainly and manifestly as the result of an inquiry into things. We can not fail to see that there is a wide difference between the proofs of geometry and the conclusions arrived at in practical engineering. Nor has the Empirical Philosophy been able either to soften or explain this distinction. The clearness of the one movement remains attributable to its purely mental character, the obscurity of the other to its dependence on the senses, to its relation to facts. Facts at once cut down the mental light.

No less distinct are the connections of judgments from the connections of facts. Thoughts cohere in