to the success of a new treatment. Every day of our lives we are
giving and receiving direct evidence; and of this evidence there is
great variety in value.

In the first place, no one should place too much reliance on his own
casual observations. It is notorious that we see what we expect to see;
and no one who has not deliberately set himself to observe the fact can
realize how much of what he thinks is observation is really inference
from a small part of the facts before him. I feel a slight tremor run
through the house with a little rattling of the windows, and assume that
a train has gone by on the railroad below the hill a hundred yards away:
as a matter of fact it may have been one of the slight earthquake shocks
which come every few years in most parts of the world. The mistakes that
most of its make in recognizing people are of the same sort: from some
single feature we reason to an identity that does not exist.

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 t