But among these shadows there can be no efficient causation. When a change takes place in the sense-compelling _universe_, the mighty machine will cast one shadow before the change and another after. The second shadow will accordingly succeed the first in orderly sequence, but the relation between the shadows is not the relation of cause and effect. Accordingly, in the laws of Nature which have been discovered by scientific investigation, we find abundant instances of unfailingly concomitant events and of uniformities of sequence, but not one single instance of cause and effect. There is nothing competent to cause one body to exclude another from the space it occupies. A statement of the fact is one of the laws of Nature. If a stone be allowed to drop in the vicinity of the earth, its downward speed is accelerated by a perfectly definite law. This law is one of the Uniformities of Nature which scientific inquiry has brought to light. But within the domain of Physics there is no cause of acceleration. The facts as to what occurs in Nature can be observed; the circumstances under which they occur can be investigated; similar cases can be compared; and the laws to which the simultaneous or successive events conform may be brought to light. But here our knowledge ends. Physical science has said its utmost. Now all this is changed when we turn to the only field of observation accessible to us in which we are dealing directly with _auta_. The _thoughts_ of which _I_ consist, the thoughts which are my _mind_, are _auta_; a very small group of _auta_, no doubt, in the mighty _Universe_, but still an actual sample, though a very special and one-sided sample of what _auta_ really are. Now in the operations that go on in my mind I do find instances, some few instances, of causes producing effects. The familiar case of a geometrical demonstration producing in a man’s mind a belief in the truth of the conclusion is a case in point. Here the understanding of the proof is the efficient cause of the belief in the conclusion which accompanies that understanding. A wish to accomplish something, and a knowledge of how to go about it, both of which are _thoughts_ in the _mind_, are a part of the efficient cause of subsequent events, unless counteracted by other causes. A few other examples can be obtained from the same small field of observation; and this is all that man, in his isolated position, has any right to expect; for the bulk of his thoughts are due, at least in large part, to autic causes which lie outside his mind, and it is there also that those of his thoughts that are known to be causes, usually exhibit their effects. When perceptions arise in my mind, the effect indeed is within my mind, but the cause is beyond it; and when I move my muscles the cause is within my mind, but it is outside the mind that it operates. The instances are indeed few where the causes and the effects are both within my tiny group of _auta_, and