So it is that mental hygiene, industrial psychology, and scientific management have a great deal in common. What, then, are the essential differences? They lie partly in the relative prominence given to particular objectives, and partly in specific techniques and methods of approach, resulting in three somewhat overlapping and yet not identical bodies of knowledge, principles, and practices. Each is valuable.

The specialist in mental hygiene, for example, trained in medical school and hospital, experienced in healing the mentally ill and in preventing nervous breakdowns, has keen eyes for conditions predisposing to anxieties and bad emotional habits. He is on the alert to diagnose and correct situations that tend to mental illness. His aim is health. Increased productivity of workers whose personalities are already well balanced is distinctly a secondary consideration. It is the problem case that first engages his attention. His typical method is that of the intimate personal interview.

The scientific-management specialist usually comes to his task with the background and training of the engineering school. He knows mechanics, economics, statistics. His eye rests on the machinery and the layout, the sales index, the production chart, and the balance sheet. He emphasizes output. His familiar tools are the slide rule and the stopwatch. Far from ignoring the human factor, he sees it as one of several important terms in his equation. His knowledge of human nature, frequently sound and shrewd, has been gained from practical experience in dealing with executives and workers in the plant. When technical or obscure questions of behavior arise, he supplements his common-sense psychology by calling upon the industrial psychologist or psychiatrist, or by instituting controlled experiments within the industrial situation and measuring the results. Indeed it is the management engineer who must be depended upon to see that the entire enterprise is so organized and administered that the staff services of industrial psychologists can function effectively.

The industrial psychologist puts the individual first, output or profits second. His training in the university laboratory and in office, store, or factory, where all sorts of workers and supervisors are employed, has impressed upon him the wide range of differences among people, in their capacities, tastes, and requirements. He knows how great is their susceptibility to training, even though they may be well on in years - provided this training is individualized and adapted to their separate needs. He has studied the springs of action and the laws governing acquisition of skill, modification of habit patterns, control of motives, and improvement of social adjustments. He, too, uses the interview, but has a predilection for checking its findings against other data and supplementing them with objective measures of performance. Indeed he is incorrigible in his insistence upon full personnel records and concrete, measurable facts. His favorite instruments are the reaction key, the kymograph, the test blank, the correlation chart. But his primary goal is not, like that of his academic colleagues, the advancement of understanding of general principles; it is effective adjustment of individual workers within their several work situations. He aims at steady increase of their earning powers up to the limits of their capacity, and at the contentment and satisfactions that can come only to those who are happily, because fittingly, employed.

The Physical and the Social Environment. Psychologists have taken their techniques and point of view into mines, factories, railways, advertising agencies, farms, printing establishments, restaurants, hotels, and aviation fields. They have studied workers and managers in textile mills, machine shops, telephone exchanges, banks, museums, libraries, laundries, and power plants. In government departments and public utilities, as well as in private industries and stores, they have analyzed work processes and the conditions that affect individual variations in performance. They have studied the abilities and aptitudes as well as the duties and difficulties of the men and women there employed. Improvements have been made so that the work could be done better, with less expenditure of energy. Appliances, tools, and benches have been adapted to the requirements of the human organism. Standards of ventilation and lighting have been modified, to remove discomfort and strain. In a wide variety of situations, the mental effects of physical working conditions have been scrutinized in the interest of greater comfort, convenience, ease, and accuracy of work.

Not only the material surroundings have received attention; the personal environment also has been studied - the psychology of supervision and of relations between fellow workers. Nothing affects a man's mental attitude more intimately than his contacts with his immediate superior. So techniques of training and of personal leadership have been investigated, and sound principles embodied in courses for supervisors, foremen, and managers, with the result that the general level of supervisory practice in industry is being steadily raised. Reasons for workers' restriction of output have been investigated. Obscure and unsuspected causes of slackness and indifference have been uncovered. The values of group incentives to teamwork have been demonstrated in particular instances. Attention has been drawn again and again to the possibility that familiar but often overlooked assets can be capitalized when workers are given a real opportunity to contribute their own ideas, share responsibility for those aspects of the enterprise closest to them, and feel a pride in its success. To be competent in one's job is indispensable; but to see this job in its total setting and to receive from one's fellows a recognition of its worthwhileness are also essential, if the will to work is to be fully released.

Such basic hypotheses about human nature in relation to both the physical and the social aspects of work, it has been the duty of industrial psychology to investigate and to apply.

Measuring Mental Attitudes, Interests, and Abilities. One way of bringing different components of the total work situation into correct perspective has been for the industrial psychologist to measure employee attitudes toward the firm's personnel policies and practices. More than seventy years have passed since Fechner laid the corner stone of experimental psychology by demonstrating the possibility of mental measurement and formulating the fundamentals of method; but only within the past decade have these methods been adapted and applied to the practical task of measuring such industrially important quantities as group morale, good will, and employee preference for various features of management practice. These techniques constitute a real contribution of psychology to industry.