inventors in the typewriter field. French authors Henri Dupont and C. Senechal described Burt's typographer in great detail in their 1906 book Patent The machine was a rectangular wooden box wide, high, and long. It mechanically worked by depressing a rotating lever so that an inked letter made contact with paper. A gauge that was designed in a circular clockwise fashion on the front of the box indicated the number of lines typed on the blank piece of paper that was up to 15 inches in length. The paper was attached to a velvet-like material belt. The belt rotated when the impression lever was depressed. Four classes of typewriters had been recognized by the U. S. Patent Office. The first was an index-wheel machine, like that patented by Burt on July 23, 1829. The second was the bar-machine first patented by John B. Fairbanks on September 17, 1850. The third was the plate-machine first patented by Oliver T. Eddy on November 12, 1850. The fourth was the key-wheel machine first patented by John Pratt on August 11, 1868. A complete working model of Burt's "typographer" was in the model room of the Patent Office from the time of the patent until the Patent Office fire of December 15, 1836. The fire destroyed all the patents and patent models issued from 1790. A competent mechanic can build a working replica of Burt's typographer from his patent description and drawings. Austin Burt, the great grandson of Burt, built a working model in 1892 for the World's Columbian Exposition working from a parchment copy of the original patent (No. 5581X). The reason Burt built the machine was to speed up his work in official correspondence as a government surveyor. John Pitts Sheldon of the Detroit Free Press, Burt's newspaper editor friend, furnished the typeface letters from the newspaper company in May 1829 for Burt's first typographer to be able to type the first letter ever written on it. The letter was to future president Martin Van Buren then Secretary of State. Two months later it received an official patent as one of the most unique and useful inventions of the time. It was the first patent for a type writing machine. Burt built in 1830 a second improved typographer typewriter that resembled a pinball machine because four tapered legs for standing were added to it. Sheldon had taken Burt's "moddle" to the Patent