No. 4.] EVOLUTION OF FARM MACHINES. 249 



law of the survival of the fittest, this invention prevailed and 

 gradually replaced the old wooden plows. Mr. Joel Nourse, 

 in 1842, improved upon the plow and brought out his famous 

 Eagle plows, that became very popular and reached a sale of 

 twenty-five to thirty thousand in one year. He made his 

 mold-board larger, with more abrupt curve in the rear part, 

 thoroughly inverting and breaking up the furrow. 



Hon. Frederick Holbrook, afterwards war governor of 

 Vermont and professor of agriculture at Cornell University, 

 invented improvements on the plow during the period from 

 1850 to 1860. He constructed plows with difierent mold- 

 boards for difierent conditions of soil, brought out the sod 

 and subsoil and swivel plow. The sod and subsoil plow of 

 Holbrook's, as in the Michigan plow of Aaron Smith, was a 

 small plow with a fin share in front of the main plow, and 

 was designed to accomplish what is now better and more 

 easily done by the jointer, introduced by James Oliver of 

 South Bend, Ind., who, after many years of experiment, 

 perfected a process of chilling and toughening iron to make 

 it suitable for the mold-board. This invention, and that by 

 John Lane of Chicago of what is known as soft-centre steel, 

 has revolutionized plow making, and almost wholly driven 

 cast iron out of the field. 



Swivel Plows. 

 The first plow to turn all furrows one way was called the 

 turn and rest plow. It was nothing more than a simple 

 wedge, made to turn on a pivot and governed by an arc in 

 the back part, passing through a slot in the handles for 

 changing. In this form each side became alternately land 

 side and mold-board. The form invented by Governor 

 Holbrook, with one mold-board, and sole and land side alter- 

 nating, and, as modified and improved by later inventors, is 

 the prevailing form now in use, and is so well liked that its 

 use in preference to the right-hand plow is increasing. 



Line of Draft. 

 It is evident that the plow in passing through the soil en- 

 counters resistance from three directions, — from the bottom 

 of the furrow, from the land side and from the furrow slice. 



