In order to demonstrate the principle of this kind of psychotechnical help with fuller detail, at least by one illustration, I may discuss the case of the advertisements, the more as this problem has already been taken up in a somewhat systematic way by the psychological laboratories.  We have a number of careful experimental investigations referring to the memory-value, the attention-value, the suggestion-value, and other mental effects of the printed business advertisements.  Of course this group of experimental investigations at once suggests an objection which we cannot ignore.  A business advertisement, as it appears in the newspapers, is such an extremely trivial thing and so completely devoted to the egotistical desire for profit that it seems undignified for the scientist to spend his time on such nothings and to shoot sparrows with his laboratory cannon-balls.  But on the one side nothing can be unworthy of thorough study from a strictly theoretical point of view.  The dirtiest chemical substance may become of greatest importance for chemistry, and the ugliest insect for zooelogy.  On the other side, if the practical point of view of the applied sciences is taken, the importance of the inquiry may stand in direct relation to the intensity of the human demand which is to be satisfied by the new knowledge.  Present-day society is so organized that the economic advertisement surely serves a need, and its intensity is expressed by the well-known fact that in every year billions are paid for advertising.  Measured by the amount of expenditure, advertising has become one of the largest and economically most important human industries.  It is, then, not astonishing that scientists consider it worth while to examine the exact foundations of this industry, but it is surprising that this industry could reach such an enormous development without being guided by the spirit of scientific exactitude which appears a matter of course in every other large business.  As it is a function of science to study the physics of incandescent lamps or gas motors so as to bring the economically most satisfactory devices into the service of the community, it cannot be less important from the standpoint of national economics to study scientifically the efficiency of the advertisements in order that the national means may in this industry, too, secure the greatest possible effects.  It is only a secondary point that experiments of this kind are of high interest to the theoretical scientist as well.  For us the advertisement is simply an instrument constructed to satisfy certain human demands by its effects on the mind.  It is a question for psychology to determine the conditions under which this instrument may be best adapted to its purpose.