Ignorance of the basic principles of music reading was one of the primary obstacles to the improvement of congregational singing in nineteenth-century America. Six separate numeral notation systems arose to provide a simple way for the common man to learn the basic principles of music. Hartley Day developed his own numeral notation system and published six tune-books that enjoyed modest success in the New England area. This thesis examines Day's numeral notation system as it appeared in the Boston Numeral Harmony (1845), and the One-Line Psalmist (1849). It also studies Day's periodical, The Musical Visitor, in which he continually attacked Lowell Mason, possibly leading to Mason's dismissal as Superintendent of Music of Boston's public schools.