Of recent years psychologists have set themselves to getting some accurate facts as to this inaccuracy of human observation, and various experiments have been tried.  Here is an account of one: 

There was, for instance, two years ago in Goettingen a meeting of a scientific association, made up of jurists, psychologists, and physicians, all, therefore, men trained in careful observation.  Somewhere in the same street there was that evening a public festivity of the carnival.  Suddenly, in the midst of the scholarly meeting, the doors open, a clown in highly colored costume rushes in in mad excitement, and a negro with a revolver in hand follows him.  In the middle of the hall first the one, then the other, shouts wild phrases; then the one falls to the ground, the other jumps on him; then a shot, and suddenly both are out of the room.  The whole affair took less than twenty seconds.  All were completely taken by surprise, and no one, with the exception of the president, had the slightest idea that every word and action had been rehearsed beforehand, or that, photographs had been taken of the scene.  It seemed most natural that the president should beg the members to write down individually an exact report, inasmuch as he felt sure that the matter would come before the courts.  Of the forty reports handed in, there was only one whose omissions were calculated as amounting to less than twenty per cent of the characteristic acts; fourteen had twenty to forty per cent of the facts omitted; twelve omitted forty to fifty per cent, and thirteen still more than fifty per cent.  But besides the omissions there were only six among the forty which did not contain positively wrong statements; in twenty-four papers up to ten per cent of the statements were free inventions, and in ten answers—­that is, in one fourth of the papers—­more than ten per cent of the statements were absolutely false, in spite of the fact that they all came from scientifically trained observers.  Only four persons, for instance, among forty noticed that the negro had nothing on his head; the others gave him a derby, or a high hat, and so on.  In addition to this, a red suit, a brown one, a striped one, a coffee-colored jacket, shirt sleeves, and similar costume were invented for him.  He wore in reality white trousers and a black jacket with a large red neck-tie.  The scientific commission which reported the details of the inquiry came to the general statement that the majority of the observers omitted or falsified about half of the processes which occurred completely in their field of vision.  As was to be expected, the judgment as to the time duration of the act varied between a few seconds and several minutes.[16]

Another type of cases in which our direct testimony would be valueless is legerdemain:  we think that we actually see rabbits taken out of our neighbor’s hat, or his watch pounded in a mortar and presently shaken whole and sound out of an empty silk handkerchief; and it is only by reasoning that we know our eyes have been deceived.