Many advertisers adopt the policy of repeating full-page advertisements at long intervals instead of advertising in a small way continually. Laboratory tests have shown, on the contrary, that a quarter-page advertisement appearing in four successive issues of a newspaper is fifty per cent more effective than a full-page advertisement appearing only once. It does not follow, however, that an eighth-page advertisement repeated eight times is correspondingly more effective; for below a certain relative size the value of an advertisement decreases much more rapidly than the cost. There are, of course, modifying conditions, such as special sales of department stores, where occasional displays and announcements make it desirable to use either full pages, or even double pages, but the great bulk of advertising is not of this character. [Sidenote: _Ratio of Size to Value_] Every year in the United States alone six hundred millions of dollars are expended in advertising the sale of commodities, and for the most part expended in a haphazard, experimental and unscientific way. The investment of this vast sum with risk of perhaps total loss, or even possible injury, through the faulty construction or improper placing of advertisements should stimulate the interest of every advertiser in the work that psychologists have done and are doing toward the accumulation of a body of exact knowledge on this subject. [Sidenote: _Risks in Advertising_] THE SCIENCE OF FORGETTING [Illustration: TESTING THE MEMORY WITH PROFESSOR JASTROW'S MEMORY APPARATUS PRIVATE LABORATORY, SOCIETY OF APPLIED PSYCHOLOGY] [Illustration: Decorative Header] CHAPTER V THE SCIENCE OF FORGETTING [Sidenote: _The Skilled Artisan_] Attention is the instrumentality through which the Laws of Recall operate. Wittingly or unwittingly, consciously or unconsciously, every man's attention swings in automatic obedience to the Laws of Recall. Attention is the artisan that, bit by bit, and with lightning quickness, constructs the mosaic of consciousness. Having the whole vast store of all present and past experiences to draw upon, he selects only those groups and those isolated instances that are related to our general interests and aims. He disregards others. [Sidenote: _How the Attention Works_] The attention operates in a manner complementary to the general Laws of Recall. It is an active principle not of association, but of _dissociation_. You choose, for example, a certain aim in life. You decide to become the inventor of an aeroplane of automatic stability. This choice henceforth determines two things. First, it determines just which of the sensory experiences of any given moment are most likely to be selected for your conscious perception. Secondly, it determines just which of your past experiences will be most likely to be recalled.