In Europe I told the philosophers and scientists of materialism that the criterion of the senses is not reliable. For instance, consider a mirror and the images reflected in it. These images have no actual corporeal existence. Yet if you had never seen a mirror you would firmly insist and believe that they were real. The eye sees a mirage upon the desert as a lake of water but there is no reality in it. As we stand upon the deck of a steamer the shore appears to be moving, yet we know the land is stationary and we are moving. The earth was believed to be fixed and the sun revolving about it but although this appears to be so, the reverse is now known to be true. A whirling torch makes a circle of fire appear before the eye, yet we realize there is but one point of light. We behold a shadow moving upon the ground but it has no material existence, no substance. In deserts the atmospheric effects are particularly productive of illusions which deceive the eye. Once I saw a mirage in which a whole caravan appeared traveling upward into the sky. In the far north other deceptive phenomena appear and baffle human vision. Sometimes three or four suns called by scientists “mock suns” will be shining at the same time whereas we know the great solar orb is one and that it remains fixed and single. In brief, the senses are continually deceived and we are unable to separate that which is reality from that which is not. As to the second criterion, reason, this likewise is unreliable and not to be depended upon. This human world is an ocean of varying opinions. If reason is the perfect standard and criterion of knowledge, why are opinions at variance and why do philosophers disagree so completely with each other? This is a clear proof that human reason is not to be relied upon as an infallible criterion. For instance, great discoveries and announcements of former centuries are continually upset and discarded by the wise men of today. Mathematicians, astronomers, chemical scientists continually disprove and reject the conclusions of the ancients; nothing is fixed, nothing final; everything continually changing because human reason is progressing along new roads of investigation and arriving at new conclusions every day. In the future much that is announced and accepted as true now will be rejected and disproved. And so it will continue ad infinitum.