Water may be conveyed uphill to the house by this means, sometimes to considerable distance. The size of the ram and its power to lift water depends upon the amount of water at the spring and the number of feet of fall. In laying the small pipe, it should be placed well down under ground to keep it cool in summer and to bury it beyond the reach of winter frost. At the upper end where the water is delivered a storage tank with an overflow is necessary, so the water can run away when not being drawn for use. A constant supply through a ram demands a constant delivery. It is necessary to guard the water intake at the dam. A fence protection around the supply pool to keep live-stock or wild animals out is the first measure of precaution. A fine screen surrounding the upper end of the pipe that supplies water to the ram is necessary to keep small trash from interfering with the valves. THE FARM TRACTOR Farm tractors are becoming practical. Most theories have had a try out, the junk pile has received many failures and the fittest are about to survive. Now, if the manufacturers will standardize the rating and the important parts and improve their selling organizations the whole nation will profit. The successful tractors usually have vertical engines with four cylinders. They are likely to have straight spur transmission gears, and a straight spur or chain drive, all carefully protected from dust. And they will have considerable surface bearing to avoid packing the soil. Some tractors carry their weight mostly upon the drive wheels--a principle that utilizes weight to increase traction. Other tractors exert a great deal of energy in forcing a small, narrow front steering-wheel through the soft ground. Any farmer who has pushed a loaded wheelbarrow knows what that means. Some kerosene tractors require a large percentage of gasoline. The driver may be as much to blame as the engine. But it should be corrected. [Illustration: Figure 113.--Tractor Transmission Gear. Spur gears are the most satisfactory for heavy work.]