The surface being cleared of snow, the ice plow is set upon the ice alongside a line drawn taut in the direction in which the plowing is to be done. The ice plow, drawn by hand and guided to run parallel with the line, gives the base groove. The blade of the guide is placed in this groove, and the field is now grooved in uniform spaces in one direction. The plow makes only one cut in each groove, while the guide is attached to it. By repeating this method grooves are made crossing those first made at right angles. The guide is now removed from the plow, and by plowing back and forth the ice is grooved to the depth desired, about seven or eight inches for twelve-inch ice and two inches for six-inch ice. A channel is now opened at the foot of the incline, and a few hours work for four men, and a boy driving the horse to run the grapple, will land the ice cakes on the platform. CHAPTER VII. ARTIFICIAL ICE AND COLD AIR MACHINES. Historical Sketch--The First Ice Machine--Its Subsequent Development--Progress in the Use of Machines--The Principles Involved in their Construction--Diversity of Application--Recent Discoveries. The artificial production of cold has engaged attention from remote ages. The application of spontaneous evaporation in Eastern countries was the earliest method employed to produce ice. America has the honor of being the home of the inventors who first achieved success in making artificial ice by modern methods. Jacob Perkins, in 1834, and Professor Twinning, of New Haven, Conn., in 1850, each procured British patents. The former did not procure a patent in this country, but Professor Twinning secured one in 1853. Two years later, he had a machine in operation at Cleveland, Ohio, which produced 1,600 pounds of ice in twenty-four hours’ run. This was a favorable result from a pioneer machine of an estimated capacity of 2,000 pounds in this time. Much credit is due these early inventors, who introduced a type of machine which is now extensively employed, and is known as the compression system. In 1851, Dr. John Gorrie, of New Orleans, La., patented a machine for producing ice, by compressing and expanding atmospheric air. This machine was also the pioneer of its class. It gave rise to what are known as air machines, used in England and on the Continent, and extensively employed for facilitating the transportation of fresh beef and mutton on the ocean. In 1848, Ferdinand Carré, of France, contrived an original process for employing aqua ammonia. In 1865 he patented an ice machine, and at the French International Exposition, in 1867, daily produced six tons of ice. This has proved to be a notable invention, the present absorption system being based upon it and extensively used.