Popular Science Monthly 



553 



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. 



