He considers several categories of deaf. Children whose disability is total and the mentally deficient have less chance for a normal life than those who maintain a rudimentary hearing and can speak.
The spoken language is faster than writing. Malling-Hansen invents as early as 1865 a writing ball that partially offsets this difference of speed and allows his pupils to participate in some sort of discussion. The spherical shape of the keyboard is due to the fact that all keys converge to the same point of the moving paper. The inventor filed a patent in 1870 and started a commercial production.
He is the undisputed pioneer in this field. His predecessors had not achieved more than poorly working prototypes. The writing ball of Malling-Hansen is however a complex machine whose manufacture is difficult and an industrialization is not realistic. Despite several awards in industrial expositions it can not compete with the type-writer with a flat keyboard invented by Sholes and Glidden, patented in 1868 and produced by Remington from 1873.
A Malling-Hansen writing ball was sold for € 100K before fees by Auction Team Breker in Cologne on May 21, 2016. Another example manufactured in 1872 is sold with its box on November 5 by the same auction house. It is estimated € 70K, lot 0108 here linked from LiveAuctioneers bidding platform.
SOLD for € 70K before fees