All beliefs as to simple matter of fact must rest ultimately on observation. But, of course, we believe many things to have happened that we have never seen. As Chaucer says:-- But God forbede but men shoulde 'lieve Wel more thing than men han seen with eye. Man shall not weenen everything a lie But if himself it seeth or else doth. For the great bulk of matters of fact that we believe we are necessarily dependent on the observations of others. And if we are to apply scientific method to the ascertainment of this, we must know what errors we are liable to in our recollections of what we have ourselves witnessed, and what errors are apt to arise in the tradition of what purports to be the evidence of eye-witnesses. I.--PERSONAL OBSERVATION. It is hard to convince anybody that he cannot trust implicitly to his memory of what he has himself seen. We are ready enough to believe that others may be deceived: but not our own senses. Seeing is believing. It is well, however, that we should realise that all observation is fallible, even our own. Three great besetting fallacies or tendencies to error may be specified:-- 1. Liability to have the attention fastened on special incidents, and so diverted from other parts of the occurrence. 2. Liability to confuse and transpose the sequence of events. 3. Liability to substitute inference for fact. It is upon the first of these weaknesses in man as an observing machine that jugglers chiefly depend on working their marvels. Sleight of hand counts for much, but diverting the spectator's eyes for a good deal more. That is why they have music played and patter incessantly as they operate. Their patter is not purposeless: it is calculated to turn our eyes away from the movements of their nimble hands. It must be borne in mind that in any field of vision there are many objects, and that in any rapid succession of incidents much more passes before the eyes than the memory can retain in its exact order. It is of course in moments of excitement and hurry, when our observation is distracted, that we are most subject to fallacious illusions of memory. Unconsciously we make a coherent picture of what we have seen, and very often it happens that the sequence of events is not what actually passed, but what we were prejudiced in favour of seeing. Hence the unlikelihood of finding exact agreement among the witnesses of any exciting occurrence, a quarrel, a railway accident, a collision at sea, the incidents of a battle.