o the market, as with a high degree of carelessness
one economic rival may be taken for another, even if the new
typewriter or the new pencil has a new form and color and name. On the
other side, the purchaser could never have a feeling of security if
imitations were considered as still legally justifiable when the
difference is so small that it needs an intense mental effort and
careful examination of details to notice it.

The result is that the jurisdiction fluctuates between these two
extremes in a most alarming way, and this seems to hold true in all
countries. In theory: "There is substantial agreement that
infringement occurs when the marks, names, labels, or packings of one
trader resemble those of another sufficiently to make it probable that
ordinary purchasers, exercising no more care than such persons usually
do in purchasing the article in question, will be deceived." But it
depends upon the trade experts and the judges to give meaning to such
a statement in the particular case, as the amount of care which
purchasers usually exercise can be understood very differently.
Sometimes the customer is expected to proceed with an attention which
is most subtly adjusted to the finest differences, and sometimes it is
taken for granted that he is unable to notice even strong variations.
It is clear that this uncertainty which disturbs the whole trade
cannot be eliminated as long as the psychological background has not
been systematically studied. Mere talking about the attention of the
customer, and his ability to decide and select, and of his
observations and his habits in the spirit of popular common-sense
psychology, can never secure exact standards and definite demarcation
lines. The question is important not only where imitations of morally
doubtful character are in the market. Even the most honest
manufacturer is in a certain sense obliged to imitate his
predecessors, as they have directed the taste and habits of the
public in particular directions, and as the product of his company
would suffer unnecessarily if he were to disregard this psychical
attitude of the prospective customers. The economic legal situation
accordingly suggests the question whether it would not be possible to
devise methods for an exact measurement of the permissible similarity,
and this demand for exactitude naturally points to the methods of the
psychological experiment. E.S. Rogers, Esq., of Chicago, who has
thoroughly discussed the l