There should be no hesitation in coming down to low speed when the engine shows by its laboring that the effort of working on high gear is becoming too great. The engine cannot deliver its full power unless its speed is maintained, and low gear is provided for those times when the load is too great to be handled on high. Use high speed whenever it is possible, but trying to force the tractor to run on high with too great a load will lead to a breakdown. High speed should be used for light work or for moving from place to place, but the engine should never be run at a greater number of revolutions than that specified by the manufacturers. It is very poor policy to run the tractor fast over rough roads, as the pounding will inevitably injure it. Cold weather changes conditions in the handling and operation of a tractor; there is difficulty in starting, lubrication is likely to be faulty, and there is danger of breakage in engine, radiator, and air washer through freezing. Difficulty in starting comes from the use of the usual medium grade of gasoline, which is satisfactory in mild weather, but will not vaporize at low temperatures. Cold gasoline will not vaporize in a cold engine; to form a mixture it is necessary to use high test gasoline, which will vaporize at low temperatures, or to warm the engine to a temperature at which medium grade gasoline will vaporize. It is advisable to keep on hand a few gallons of high test gasoline to use in starting, or even a mixture of high test gasoline and ether, half-and-half, for extreme cold weather. The engine may be warmed by pouring a bucket of hot water into the cooling system, cranking the engine to get it into the water jackets of the cylinders. Another plan is to wrap cloth around the intake manifold and carburetor, soaking it with hot water, being careful not to get water into the air intake. A drop of liquid gasoline on the points of the spark plug will short-circuit them and prevent the formation of a spark; the points should be dry, and it is an advantage to heat the plugs, screwing them hot into the engine at the last moment before trying to start. Kerosene is thicker when cold than when warm; it will not flow so freely, and the needle valve of the carburetor must be opened more in winter than in summer to obtain a proper mixture. Lubricating oil also thickens in cold weather, and flows much more sluggishly. The lubrication adjustments that are correct for summer will therefore be incorrect for winter. This may be provided for to a great extent by using a thinner oil in winter than the oil used in summer. A cold snap is likely to result in burned bearings if the change in lubrication that it brings is not allowed for. Grease thickens in cold weather more than oil does, and some kinds freeze solid. In winter a light, soft grease should be used, and the grease cups should be turned down several more turns than is usual when the weather is warm.