The counters, shelves, or tables should be so built as to bring the objects on them as nearly as possible on a level with the eye, at the same time without cutting off the view of wall exhibits. The height and dimensions of the counters shown opposite page 85 were worked out carefully to meet this condition. It is always a good thing to have a railing separate visitors from the exhibits as more people can see them if all are held back from pressing too closely. Another important consideration in placing exhibits is that they should not be crowded. When objects or placards crowd one another it becomes impossible to look at one thing without having others in the margin of vision interfere with concentrated attention. The first impression of a crowded car is one of bewilderment. The visitor is obliged not only to grasp new ideas and facts presented in an unfamiliar form, but to select among a large number those of special interest to him. ARRANGEMENT OF SUBJECT MATTER Because of the small space and necessarily quick movements of visitors, it is especially important that exhibits should be arranged in some logical sequence. Visitors are sometimes called upon to perform amazing feats in mental acrobatics, leaping from one topic to another with breathless speed. For example, in the exhibit pictured opposite page 84, we see a poster about baby deaths resting on a model of a school building with a placard nearby urging the use of schools as community centers. Across the narrow aisle is a model obviously unrelated either to community centers or baby deaths. The sequence of ideas should be such that each new thought is made easier to understand and more interesting because of what went before it, or each separate exhibit should be clearly related to one central idea. Thus, in the first exhibit of the Pennsylvania Food Conservation Train the series of topics was developed as follows: Why we must save Small savings Saving wheat Saving sugar Saving fats Using all the milk Using home products. Not only the sequence of ideas but the separation between two topics is important. This can be accomplished by a visible separation, allowing a distance of at least six inches between exhibits relating to different topics; better still, by putting up actual barriers between the exhibits, as is done in the exhibit opposite page 70. The barrier has the advantage of holding the eye at one spot, so that there is no temptation to desert one exhibit for the lure of a bright color or a curious device farther on.