The explanation of this decrease in the proportion of the population that is engaged in agriculture is twofold; the first is the real increase in the productive output per person in agricultural industry. In larger part this is due to the increasing use of machinery in place of simple hand tools, and the substitution of horse-, hydraulic-, windmill-, steam-, and gasoline-power for human labor. This change has been made readily in the regions of level fields, but of late has been made possible to a greater extent in hilly country, by rearranging and combining the old irregular fields into regular fairly level rectangular fields easily tillable, while turning the rougher lands and hillsides into wood lots and pastures.[5] One man, thus, driving three or four or more horses, can do the work formerly done by two or more men and do it just as well. The farmers' incomes in different parts of the country vary pretty nearly with the amount of horse-power used per man. Economies equally great are made in the work done in the barnyards and barns. In most parts of the country only a beginning has been made in these ways, and in future the census will continue to reflect the progress in these directions. § 7. #Transfer of work from farm to factory#. The other part of the explanation of the decrease in the proportion of the population that is engaged in agriculture is that many operations are, step by step, being transferred from the farm to the factory. "Agriculture," we have observed, is a great complex of industries, in which many different products are taken from the first simplest extractive stage, and then put through successive processes to make them more nearly fitted for their final uses. Not so long ago grain cut in the field was threshed, winnowed, shelled, made into flour, and baked on the farm, as it still is in many places. Logs were cut into boards, planed, and made into houses or furniture by the farmer. The old-time farmer made by hand a large number of his farm implements--rakes, ax handles, pumps, carts, and even wagons. Until a generation ago all butter, cheese, and other dairy products were made on the farm. Now these things are being done in steadily increasing proportion by workers classified as in the manufacturing industries, and agriculture contains fewer separate industries and processes. Of course there is economy of labor in nearly all of these changes, but the number occupied in agriculture is greatly reduced. Many farmers and more farmers' sons are moving from agriculture into occupations of manufacturing, trade, transportation, and the professions, and are becoming more narrow specialists.