Unfortunately, the things that cannot be shown in any easily intelligible way surpass in importance the items that can be shown. The sheep shears, which anyone can understand, represent less to the farmer than do the sheep. Sheep shears, no matter how sophisticated and no matter how necessary, do not explain sheep husbandry. The shears tell little about the wool industry, and nothing much about sheep breeds. And so on through the list of agricultural enterprises. Museums must collect and exhibit the tools, implements, and machines which farmers use in their business. These items, however, seldom make up the core of real agricultural activity. The catalog here presented shows something of the range of items that farmers use and that can be preserved and shown. The variety nearly equals the volume. Most museums try to avoid duplication. Even so, few museums manage to collect a continuous series of things showing any one line of development. The discontinuity of farm objects on hand virtually rules out the telling of a coherent and complete history of agriculture. Nevertheless, the museum can show something about the major technological developments in agriculture. The evolution of the plow, the reaper, or the tractor can be suggested even if not fully illustrated. Hitting the highlights has to suffice. The full history of technological change also involves several social and economic conditions. First, changes in implements, tools, and methods result from the accumulation of knowledge. Device builds upon device: first came the wheel, and then, much later, the tractor. Secondly, the potential user of the device must feel a need for it. The new method or device not only must save him work but must clearly increase his well-being. If any device or change merely increases the wealth of someone else (a tax collector or a landlord for example), the farmer seldom will adopt the new technology. Thirdly, since, at first, the new technology almost invariably costs more than the old, the user must have or be able to get the capital to buy and use the newer devices and methods. Of these conditions for technological change, only the cumulative nature of the knowledge can be shown by the objects. Even here, however, missing objects make it possible to present only the most obvious changes, and then not all of them. Still, seeing the things once used--no matter how crude or how few--can sometimes help us understand the way changes took place. Also, this knowledge sometimes can help us guess how other changes will take place: