But even in places where division of labor is stimulated by demand, it can go no further than the number of distinct motions required in carrying through the manufacture of the article made. Indeed, economy requires that each motion should make a complete round, so that the work begins and ends for each worker with everything in the same position. The exception is when a motion with great exertion requires an interval of rest before a second. Two men with a cross-cut saw, although their motions are alike, do more than twice as much as one man, because of the relief in pushing back the saw. A most important limit, however, is made by the inconstancy of natural forces employed in any industry. This is notable in all the processes of agriculture. No matter how many workers combine in raising field crops, they can gain but few advantages from dividing their tasks minutely. Each laborer must be employed through the year, and the change of seasons requires that he be ready for all the operations of the different seasons in planting and tilling and gathering through all the succession. Ordinary changes of weather, cold or hot, wet or dry, windy or calm, make necessary changes in his labor. The uncertainties of each year as to moisture and heat require a variety of ventures, so that no farmer dares confine himself to raising but a single crop. Even under the most favorable conditions the different stages of growth are so intimately related that the watchfulness of the same interested manager is required at every stage. A delicate plant must be carried delicately, even in transplanting. More important still are the conditions of fertility, which make a rotation of crops and even mixed farming essential to highest productiveness. If each field must have its definite series of cropping and tillage, together with the application of animal manures, the advantage of these combined operations under the oversight and labor of a single farmer outweighs the advantage of more perfect division of labor. The result of all these limitations, so obvious in agriculture, is that farm work is but slightly more effective or more continuous than it was hundreds of years since. While improved machinery has immensely reduced the cost of certain processes, a year’s labor involves innumerable changes of employment, so that no farmer inquires, in hiring his help, for an expert in any direction, but wants a man of all work whose skill is largely ingenuity in adjusting himself to the constantly changing duties.