Page:Popular Science Monthly Volume 88.djvu/581

 Popular Science Monthly

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���Bring the fresh air to your pillow, and avoid danger and the annoyance of getting up in the cold to close the window in the morning

��soil and its physical condition. A two- plow tractor, therefore, should have an effective drawbar pull of one thousand to one thousand two hundred pounds, re- gardless of the speed at which it travels.

As the effective pull of a round-wheel tractor is seldom over one-fourth to one- third its total weight, it is hardly feasible to build the conventional tractor with much less than two tons of weight. In present quantities, well-built tractors of this size can seldom be sold for less than fifteen to twenty cents per pound.

The problem of the light tractor de- signer has, therefore, been complicated by factors of cost and mechanical eiifi- ciency which have made progress very slow.

Besides the wheel-type of tractor there is another class using either one or two endless steel belts. The "caterpillar" type, so-called from the trade name of a leading example, has peculiar advantages in the small-unit field in that it can be built narrow, with a low center of grav- ity, and still obtain an enormous grip upon the soil owing to the length and breadth of its track in contact with the ground. Very successful small tractors of this type are in common use, and the earlier disadvantage of extreme wear on the tracks has apparently been overcome by the use of good material and ingenious construction. The tractive efficiency is

��high in proportion to weight and motor power, steering is easily accomplished, and on either soft or hard ground the broad surface of the track has obvious advantages.

Still another type, as yet of little com- mercial importance, discards the plow and uses instead a rotary cylinder, studded with flexible steel hooks to pulverize the soil. An ordinary tractor chassis of light weight is used, the cylin- der requiring practically no assistance from the drive-wheels in its forward motion. In fact, tests have sometimes shown that the cylinder helps to propel the entire machine.

A Fresh-Air Funnel for Your Bedroom

THOSE who are too timorous to brave a widely opened window in the bedroom may have their supply of fresh air brought to them without ex- posure by the window-fitting illustrated.

The device is in reality a fresh-air tunnel made of light fabric and held in place by hoops of metal to insure an open air passage at all times when the air-chute is in use. At one end the chute opens through a window-board, thus admitting the fresh air. The other end is draped over the head of the bed;

The air-chute may be opened or closed by means of a string.

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